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@layer reset, tokens, base, layout, components, utilities;
@layer tokens {
:root {
  color-scheme: light;

  /* Neutral surfaces keep the visual impression of white without using a hard white. */
  --color-canvas: oklch(0.992 0.004 250);
  --color-surface: oklch(0.997 0.003 250);
  --color-surface-subtle: oklch(0.974 0.01 248);
  --color-surface-selected: oklch(0.947 0.028 245);
  --color-ink: oklch(0.27 0.012 255);
  --color-ink-strong: oklch(0.18 0.014 255);
  --color-text-muted: oklch(0.48 0.012 255);
  --color-text-faint: oklch(0.61 0.012 255);
  --color-line: oklch(0.9 0.008 250);
  --color-line-strong: oklch(0.81 0.014 250);

  --color-blue-500: oklch(0.69 0.165 246);
  --color-blue-600: oklch(0.59 0.17 250);
  --color-blue-700: oklch(0.48 0.15 254);
  --color-blue-800: oklch(0.39 0.13 256);

  --color-success: oklch(0.5 0.13 145);
  --color-success-surface: oklch(0.97 0.025 145);
  --color-success-line: oklch(0.78 0.08 145);
  --color-warning: oklch(0.49 0.1 74);
  --color-warning-surface: oklch(0.975 0.035 82);
  --color-warning-line: oklch(0.8 0.08 82);
  --color-danger: oklch(0.48 0.17 27);
  --color-danger-surface: oklch(0.97 0.025 24);
  --color-danger-line: oklch(0.79 0.08 24);

  /* A build profile may override only this brand layer. */
  --brand-action: var(--color-blue-600);
  --brand-action-hover: var(--color-blue-700);
  --brand-action-active: var(--color-blue-800);
  --brand-action-soft: var(--color-surface-selected);
  --brand-on-action: oklch(0.985 0.004 250);
  --brand-focus-ring: color-mix(in oklch, var(--brand-action) 34%, transparent);
  --brand-lockup-wide-max: 10.5rem;
  --brand-lockup-compact-size: 2rem;

  --font-sans: Inter, ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  --font-mono: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
  --font-math: KaTeX_Main, "Times New Roman", serif;

  --text-xs: 0.75rem;
  --text-sm: 0.875rem;
  --text-base: 1rem;
  --text-lg: 1.125rem;
  --text-xl: 1.25rem;
  --text-2xl: 1.5rem;
  --text-3xl: 1.875rem;
  --text-4xl: 2.25rem;
  --text-5xl: 3rem;

  --leading-tight: 1.15;
  --leading-heading: 1.24;
  --leading-body: 1.65;

  --weight-medium: 560;
  --weight-semibold: 650;
  --weight-bold: 740;
  --weight-heavy: 800;

  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;
  --space-20: 5rem;
  --space-24: 6rem;

  --radius-sm: 0.5rem;
  --radius-md: 0.8rem;
  --radius-lg: 1.2rem;
  --radius-pill: 100vmax;

  --shadow-menu: 0 1rem 2.5rem oklch(0.18 0.014 255 / 0.11);
  --shadow-floating-tool: 0 0.75rem 2rem oklch(0.18 0.014 255 / 0.08);

  --page-gutter: clamp(1rem, 4vw, 2.5rem);
  --content-wide: 88rem;
  --content-reading: 52rem;
  --content-narrow: 42rem;
  --article-gap: clamp(2rem, 6vw, 5rem);
  --control-height: 2.75rem;
  --header-height: 4.5rem;

  --duration-fast: 140ms;
  --duration-standard: 190ms;
  --ease-out: cubic-bezier(0.22, 1, 0.36, 1);

  --z-header: 20;
  --z-menu: 30;
  --z-skip-link: 100;
  --z-floating-tool: 1000;
}

@media (max-width: 35rem) {
  :root {
    --header-height: 4rem;
    --text-5xl: 2.25rem;
    --text-4xl: 1.875rem;
    --text-3xl: 1.625rem;
  }
}

@media (max-width: 22rem) {
  :root {
    --text-5xl: 2rem;
  }
}

}
@layer base {
*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--color-canvas);
  color: var(--color-ink);
  font-family: var(--font-sans);
  font-size: var(--text-base);
  line-height: var(--leading-body);
  -webkit-font-smoothing: antialiased;
}

[hidden] {
  display: none !important;
}

main,
header,
footer,
section,
article,
aside,
nav {
  min-width: 0;
}

h1,
h2,
h3,
h4 {
  color: var(--color-ink-strong);
  font-weight: var(--weight-bold);
  letter-spacing: -0.025em;
  line-height: var(--leading-heading);
  text-wrap: balance;
}

h1 {
  margin-block: 0;
  font-size: var(--text-5xl);
}

h2 {
  margin-block: 0 var(--space-5);
  font-size: var(--text-4xl);
}

h3 {
  margin-block: 0 var(--space-2);
  font-size: var(--text-xl);
}

h4 {
  margin-block: 0 var(--space-2);
  font-size: var(--text-lg);
}

p,
ul,
ol,
dl,
figure,
blockquote {
  margin-block: 0 var(--space-4);
}

ul,
ol {
  padding-inline-start: 1.25rem;
}

a {
  color: var(--brand-action-hover);
  text-decoration-thickness: 0.08em;
  text-underline-offset: 0.2em;
}

a:hover {
  color: var(--brand-action-active);
}

img,
svg,
video,
canvas {
  display: block;
  max-width: 100%;
}

button,
input,
select,
textarea,
math-field {
  font: inherit;
}

button,
summary,
a,
input,
select,
textarea,
math-field {
  -webkit-tap-highlight-color: transparent;
}

button,
input,
select,
textarea {
  accent-color: var(--brand-action);
}

button,
select,
input:not([type="checkbox"]):not([type="radio"]):not([type="range"]),
textarea,
summary {
  min-height: var(--control-height);
}

button,
summary,
select,
input[type="checkbox"],
input[type="radio"],
input[type="range"] {
  cursor: pointer;
}

button:disabled,
input:disabled,
select:disabled,
textarea:disabled {
  cursor: not-allowed;
  opacity: 0.58;
}

:focus-visible {
  outline: 3px solid var(--brand-focus-ring);
  outline-offset: 3px;
}

input:focus-visible,
select:focus-visible,
textarea:focus-visible,
math-field:focus-within {
  border-color: var(--brand-action);
  box-shadow: 0 0 0 3px var(--brand-focus-ring);
  outline: 0;
}

[aria-invalid="true"] {
  border-color: var(--color-danger) !important;
}

hr {
  height: 1px;
  margin-block: var(--space-10);
  border: 0;
  background: var(--color-line);
}

table {
  border-collapse: collapse;
}

th {
  color: var(--color-ink-strong);
  font-weight: var(--weight-semibold);
  text-align: start;
}

code,
pre,
kbd,
samp {
  font-family: var(--font-mono);
}

code {
  border-radius: 0.3rem;
  background: var(--color-surface-subtle);
  box-decoration-break: clone;
  padding: 0.12em 0.32em;
  font-size: 0.9em;
}

pre {
  max-width: 100%;
  overflow: auto;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  padding: var(--space-4);
}

math-field,
math-tex,
.katex {
  color: var(--color-ink-strong);
}

math-tex[display],
.katex-display,
.math-display {
  display: block;
  max-width: 100%;
  margin-block: var(--space-5);
  overflow-x: auto;
  overflow-y: hidden;
  overscroll-behavior-inline: contain;
  padding-block: var(--space-1);
}

::selection {
  background: var(--brand-action-soft);
  color: var(--color-ink-strong);
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
  }
}

}
@layer layout {
.page-shell {
  width: min(100%, var(--content-wide));
  margin-inline: auto;
  padding-inline: var(--page-gutter);
}

.page-shell--reading {
  width: min(100%, calc(var(--content-reading) + 2 * var(--page-gutter)));
}

.page-shell--narrow {
  width: min(100%, calc(var(--content-narrow) + 2 * var(--page-gutter)));
}

.site-header {
  position: relative;
  z-index: var(--z-header);
  border-block-end: 1px solid var(--color-line);
  background: color-mix(in oklch, var(--color-surface) 96%, transparent);
}

.site-header__inner {
  min-height: var(--header-height);
  display: flex;
  align-items: center;
  gap: var(--space-6);
}

.site-header__brand {
  flex: 0 1 auto;
}

.site-header__nav {
  margin-inline-start: auto;
}

.site-main {
  min-height: 65vh;
}

.site-footer {
  border-block-start: 1px solid var(--color-line);
  background: var(--color-surface);
  padding-block-start: var(--space-12);
}

.site-footer__inner {
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(16rem, 1fr);
  gap: var(--space-12);
}

.site-footer__nav {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: var(--space-2) var(--space-4);
  align-content: start;
}

.site-footer__meta {
  display: flex;
  justify-content: space-between;
  gap: var(--space-4);
  border-block-start: 1px solid var(--color-line);
  margin-block-start: var(--space-10);
  padding-block: var(--space-4) var(--space-6);
  color: var(--color-text-muted);
  font-size: var(--text-xs);
}

.section {
  padding-block: clamp(3rem, 6vw, 4.75rem);
}

.section--compact {
  padding-block: clamp(2.25rem, 4vw, 3.5rem);
}

.section--divided {
  border-block: 1px solid var(--color-line);
  background: var(--color-surface);
}

.surface-band {
  background: color-mix(in oklch, var(--color-surface-subtle) 62%, var(--color-canvas));
}

.page-intro {
  max-width: none;
  padding-block: clamp(2.25rem, 5vw, 4rem) var(--space-8);
}

.page-intro > h1,
.page-intro > .lede,
.page-intro > .direct-answer {
  max-width: var(--content-reading);
}

.page-intro__lede {
  max-width: 66ch;
  margin-block-start: var(--space-4);
  color: var(--color-text-muted);
  font-size: var(--text-lg);
  line-height: 1.55;
}

.page-intro .lede {
  max-width: 66ch;
  margin-block: var(--space-4) 0;
  color: var(--color-text-muted);
  font-size: var(--text-lg);
  line-height: 1.55;
}

.page-intro--task {
  padding-block-end: var(--space-5);
}

.page-intro--task .lede {
  margin-block-start: var(--space-3);
}

.section--task-tight {
  padding-block-start: var(--space-4);
}

.page-intro__meta {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2) var(--space-4);
  align-items: center;
  margin-block-start: var(--space-5);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.section-heading {
  max-width: 46rem;
  margin-block-end: var(--space-6);
}

.section-heading > :last-child {
  margin-block-end: 0;
}

.section-heading p {
  max-width: 65ch;
  color: var(--color-text-muted);
  font-size: var(--text-lg);
}

.reading-column {
  max-width: calc(var(--content-reading) + 2 * var(--page-gutter));
}

.page--topicHub .site-main .page-shell,
.page--practiceHub .site-main .page-shell {
  width: min(100%, calc(68rem + 2 * var(--page-gutter)));
}

.page--tool .site-main .page-shell {
  width: min(100%, calc(76rem + 2 * var(--page-gutter)));
}

.page--formula .site-main .page-shell {
  width: min(100%, calc(76rem + 2 * var(--page-gutter)));
}

.page--topicHub .site-main .reading-column,
.page--practiceHub .site-main .reading-column,
.page--tool .site-main .reading-column,
.page--formula .site-main .reading-column {
  max-width: none;
}

.reading-column > p,
.reading-column > ul {
  max-width: 72ch;
}

.task-hero {
  display: grid;
  grid-template-columns: minmax(17rem, 0.72fr) minmax(32rem, 1.28fr);
  gap: clamp(2rem, 5vw, 5rem);
  align-items: start;
  padding-block: clamp(2.5rem, 7vw, 5rem) clamp(4rem, 8vw, 6.5rem);
}

.task-hero__intro {
  position: sticky;
  inset-block-start: var(--space-8);
  padding-block-start: var(--space-5);
}

.task-hero__intro p {
  max-width: 60ch;
}

.focused-tool-layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(17rem, 0.42fr);
  gap: clamp(2rem, 6vw, 5rem);
  align-items: start;
}

.article-layout {
  display: grid;
  grid-template-columns: 12rem minmax(0, var(--content-reading));
  gap: var(--article-gap);
  justify-content: center;
  align-items: start;
  padding-block-end: clamp(4rem, 9vw, 7rem);
}

.article-outline {
  position: sticky;
  inset-block-start: var(--space-6);
}

.article-body {
  min-width: 0;
}

.lesson-section {
  padding-block: clamp(2.75rem, 6vw, 4.25rem);
  scroll-margin-block-start: var(--space-6);
}

.lesson-section + .lesson-section {
  border-block-start: 1px solid var(--color-line);
}

.lesson-section:first-child {
  padding-block-start: 0;
}

.article-body > section {
  padding-block: clamp(2.75rem, 6vw, 4.25rem);
  scroll-margin-block-start: var(--space-6);
}

.article-body > section + section {
  border-block-start: 1px solid var(--color-line);
}

.article-body > section:first-child {
  padding-block-start: 0;
}

.lesson-section p,
.lesson-section li {
  max-width: 72ch;
}

.article-body > section p,
.article-body > section li {
  max-width: 72ch;
}

.page--tool .page-intro {
  padding-block-end: var(--space-4);
}

.page--tool .task-section {
  padding-block-start: 0;
}

@media (min-width: 51.251rem) {
  .page--guide .page-intro {
    width: min(100%, calc(12rem + var(--article-gap) + var(--content-reading) + var(--page-gutter) + var(--page-gutter)));
    max-width: none;
    padding-inline-start: calc(var(--page-gutter) + 12rem + var(--article-gap));
  }

  .page--guide .site-main .page-shell.post-content-rail {
    width: min(100%, calc(12rem + var(--article-gap) + var(--content-reading) + var(--page-gutter) + var(--page-gutter)));
    max-width: none;
    padding-inline-start: calc(var(--page-gutter) + 12rem + var(--article-gap));
  }
}

.split-layout {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: clamp(2rem, 6vw, 5rem);
  align-items: start;
}

.reading-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(16rem, 0.45fr);
  gap: clamp(2rem, 6vw, 5rem);
  align-items: start;
}

.stack {
  display: flex;
  flex-direction: column;
  justify-content: flex-start;
}

.stack > * {
  margin-block: 0;
}

.stack > * + * {
  margin-block-start: var(--stack-space, var(--space-4));
}

.cluster {
  display: flex;
  flex-wrap: wrap;
  gap: var(--cluster-space, var(--space-3));
  align-items: center;
}

@media (max-width: 60rem) {
  .task-hero,
  .focused-tool-layout {
    grid-template-columns: minmax(0, 1fr);
    gap: var(--space-8);
  }

  .task-hero__intro {
    position: static;
    padding-block-start: 0;
  }
}

@media (max-width: 51.25rem) {
  .site-header__inner {
    gap: var(--space-3);
  }

  .site-header__nav--desktop {
    display: none;
  }

  .article-layout {
    grid-template-columns: minmax(0, 1fr);
    gap: 0;
  }

  .article-outline {
    position: static;
  }

  .split-layout,
  .reading-grid,
  .site-footer__inner {
    grid-template-columns: minmax(0, 1fr);
  }
}

@media (max-width: 40.625rem) {
  .site-footer__nav {
    grid-template-columns: minmax(0, 1fr);
  }

  .site-footer__meta,
  .page-intro__meta {
    align-items: flex-start;
    flex-direction: column;
  }
}

}
@layer components {
.skip-link {
  position: fixed;
  z-index: var(--z-skip-link);
  inset-block-start: var(--space-3);
  inset-inline-start: var(--space-3);
  transform: translateY(-180%);
  border-radius: var(--radius-sm);
  background: var(--color-ink-strong);
  color: var(--color-surface);
  padding: 0.65rem 0.9rem;
  transition: transform var(--duration-fast) var(--ease-out);
}

.skip-link:focus {
  transform: translateY(0);
}

.brand-lockup {
  min-width: 0;
  min-height: var(--control-height);
  display: inline-flex;
  align-items: center;
  gap: var(--space-3);
  color: var(--color-ink-strong);
  font-weight: var(--weight-bold);
  letter-spacing: -0.02em;
  text-decoration: none;
}

.brand-lockup__wide {
  width: auto;
  max-width: var(--brand-lockup-wide-max);
  max-height: 2rem;
  object-fit: contain;
  object-position: inline-start center;
}

.brand-lockup__compact {
  width: var(--brand-lockup-compact-size);
  height: var(--brand-lockup-compact-size);
  flex: 0 0 auto;
  object-fit: contain;
}

.brand-lockup__mark {
  width: var(--brand-lockup-compact-size);
  height: var(--brand-lockup-compact-size);
  display: none;
  flex: 0 0 auto;
  object-fit: contain;
}

.brand-lockup__name {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.brand-lockup--footer img {
  width: auto;
  max-width: var(--brand-lockup-wide-max);
  max-height: 2rem;
}

.primary-nav {
  display: flex;
  align-items: center;
  gap: var(--space-1);
}

.site-header .primary-nav {
  margin-inline-start: auto;
}

.primary-nav a {
  min-height: var(--control-height);
  display: inline-flex;
  align-items: center;
  border-radius: var(--radius-sm);
  color: var(--color-text-muted);
  padding: 0.55rem 0.8rem;
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
  text-decoration: none;
}

.primary-nav a:hover {
  background: var(--color-surface-subtle);
  color: var(--color-ink-strong);
}

.primary-nav a[aria-current="page"] {
  background: var(--brand-action-soft);
  color: var(--brand-action-active);
}

.nav-menu {
  position: relative;
  display: none;
  margin-inline-start: auto;
}

.nav-menu > summary {
  min-width: var(--control-height);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-ink);
  padding: 0.5rem 0.75rem;
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
  list-style: none;
}

.nav-menu > summary::-webkit-details-marker {
  display: none;
}

.nav-menu__panel {
  position: absolute;
  z-index: var(--z-menu);
  inset-block-start: calc(100% + var(--space-2));
  inset-inline-end: 0;
  width: min(20rem, calc(100vw - 2rem));
  display: grid;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  box-shadow: var(--shadow-menu);
  padding: var(--space-2);
}

.nav-menu:not([open]) .nav-menu__panel {
  display: none;
}

.mobile-nav {
  position: relative;
  display: none;
  margin-inline-start: auto;
}

.mobile-nav > summary {
  min-width: var(--control-height);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-ink);
  padding: 0.5rem 0.75rem;
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
  list-style: none;
}

.mobile-nav > summary::-webkit-details-marker {
  display: none;
}

.mobile-nav > nav {
  position: absolute;
  z-index: var(--z-menu);
  inset-block-start: calc(100% + var(--space-2));
  inset-inline-end: 0;
  width: min(20rem, calc(100vw - 2rem));
  display: grid;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  box-shadow: var(--shadow-menu);
  padding: var(--space-2);
}

.mobile-nav:not([open]) > nav {
  display: none;
}

.mobile-nav a {
  min-height: var(--control-height);
  display: flex;
  align-items: center;
  border-radius: var(--radius-sm);
  color: var(--color-text-muted);
  padding: 0.55rem 0.75rem;
  text-decoration: none;
}

.mobile-nav a:hover {
  background: var(--color-surface-subtle);
  color: var(--color-ink-strong);
}

.breadcrumbs {
  margin-block: 0;
  overflow-x: auto;
  padding-block: var(--space-5) 0;
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  white-space: nowrap;
  scrollbar-width: none;
}

.breadcrumbs::-webkit-scrollbar {
  display: none;
}

.breadcrumbs > ol,
.breadcrumbs:is(ol) {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin: 0;
  padding: 0;
  list-style: none;
}

.breadcrumbs a {
  color: inherit;
}

.breadcrumbs li + li::before {
  margin-inline-end: var(--space-2);
  color: var(--color-text-faint);
  content: "/";
}

.preview-notice {
  border-block-end: 1px solid var(--color-warning-line);
  background: var(--color-warning-surface);
  color: var(--color-warning);
  padding: var(--space-2) var(--page-gutter);
  font-size: var(--text-xs);
  font-weight: var(--weight-semibold);
  text-align: center;
}

.eyebrow {
  margin: 0 0 var(--space-2);
  color: var(--brand-action-active);
  font-size: var(--text-xs);
  font-weight: var(--weight-heavy);
  letter-spacing: 0.075em;
  text-transform: uppercase;
}

.section-label,
.resource-meta {
  margin: 0 0 var(--space-2);
  color: var(--brand-action-active);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
  letter-spacing: 0;
}

.button {
  min-height: 3rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  border: 1px solid transparent;
  border-radius: var(--radius-sm);
  padding: 0.68rem 1rem;
  font-weight: var(--weight-bold);
  line-height: 1.2;
  text-decoration: none;
  transition: background-color var(--duration-fast) var(--ease-out), border-color var(--duration-fast) var(--ease-out), color var(--duration-fast) var(--ease-out), transform var(--duration-fast) var(--ease-out);
}

.button:hover {
  transform: translateY(-1px);
}

.button:active {
  transform: translateY(0);
}

.button--primary {
  background: var(--brand-action-hover);
  color: var(--brand-on-action);
}

.button--primary:hover {
  background: var(--brand-action-active);
  color: var(--brand-on-action);
}

.button--secondary {
  border-color: var(--color-line-strong);
  background: var(--color-surface);
  color: var(--color-ink);
}

.button--secondary:hover {
  border-color: var(--brand-action);
  background: var(--color-surface-subtle);
  color: var(--color-ink-strong);
}

.button--quiet {
  min-height: var(--control-height);
  border-color: var(--color-line);
  background: transparent;
  color: var(--color-text-muted);
  padding: 0.5rem 0.75rem;
  font-size: var(--text-sm);
}

.button[aria-busy="true"] {
  cursor: wait;
  opacity: 0.78;
}

.text-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-weight: var(--weight-semibold);
}

.trust-line {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3) var(--space-4);
  margin-block-start: var(--space-6);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
}

.trust-line [data-icon] {
  color: var(--color-success);
  font-weight: var(--weight-heavy);
}

.direct-answer {
  max-width: 68ch;
  margin-block-start: var(--space-4);
  color: var(--color-ink-strong);
  font-weight: var(--weight-medium);
}

.after-task-summary {
  max-width: 68ch;
  margin-block: var(--space-8) 0;
  color: var(--color-text-muted);
}

.task-shell {
  min-width: 0;
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-lg);
  background: var(--color-surface);
  box-shadow: var(--shadow-floating-tool);
  overflow: clip;
}

.task-shell__form,
.task-shell__section {
  padding: clamp(1rem, 3vw, 1.75rem);
}

.task-shell__section + .task-shell__section {
  border-block-start: 1px solid var(--color-line);
}

.task-shell .solver-form {
  min-width: 0;
  padding: clamp(1rem, 3vw, 1.75rem);
}

.task-shell .solver-form textarea {
  width: 100%;
  min-height: 7rem;
  resize: vertical;
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-ink-strong);
  padding: var(--space-4);
  font-family: var(--font-mono);
  line-height: 1.5;
}

.task-shell .solver-form math-field {
  width: 100%;
  min-height: 7rem;
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-ink-strong);
  padding: var(--space-4);
  font-size: var(--text-2xl);
  --caret-color: var(--brand-action-active);
  --selection-background-color: color-mix(in oklch, var(--brand-action) 18%, transparent);
  --smart-fence-color: var(--brand-action-active);
}

.task-shell .solver-form math-field:focus-within {
  border-color: var(--brand-action);
  box-shadow: 0 0 0 3px var(--brand-focus-ring);
  outline: 0;
}

.math-keyboard-dismiss {
  position: fixed;
  z-index: 10000;
  inset-block-start: var(--space-3);
  inset-inline-end: max(var(--space-3), calc((100vw - 72rem) / 2));
  min-height: var(--control-height);
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-pill);
  background: var(--color-surface);
  box-shadow: var(--shadow-menu);
  color: var(--color-ink-strong);
  padding: 0.55rem 0.85rem;
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.coefficient-builder > .field-hint,
.structured-builder > .field-hint {
  margin-block: var(--space-2) 0;
  text-align: start;
}

.equation-preview {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  align-items: baseline;
  margin-block-start: var(--space-4);
  border-radius: var(--radius-sm);
  background: var(--color-surface-subtle);
  padding: var(--space-3) var(--space-4);
}

.equation-preview > span {
  color: var(--color-text-muted);
  font-size: var(--text-xs);
  font-weight: var(--weight-semibold);
  text-transform: uppercase;
}

.equation-preview output {
  font-family: var(--font-mono);
  overflow-wrap: anywhere;
}

.data-role-control {
  margin-block-start: var(--space-4);
}

.practice-set__header {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: var(--space-8);
  align-items: end;
  margin-block-end: var(--space-6);
}

.practice-set__header h2,
.practice-set__header p {
  max-width: 62ch;
}

.practice-progress {
  min-width: 12rem;
  display: grid;
  gap: var(--space-2);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.practice-progress progress {
  width: 100%;
  height: 0.5rem;
  accent-color: var(--brand-action);
}

.practice-question {
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-lg);
  background: var(--color-surface);
  box-shadow: var(--shadow-floating-tool);
  padding: clamp(1.25rem, 4vw, 2.25rem);
}

.practice-question__skill {
  margin: 0 0 var(--space-2);
  color: var(--brand-action-active);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.practice-question h3 {
  margin-block-end: var(--space-2);
}

.practice-question .question-formula {
  margin-block: var(--space-5);
}

.practice-answer-field,
.practice-choices {
  min-width: 0;
  display: grid;
  gap: var(--space-2);
  margin: 0;
  border: 0;
  padding: 0;
}

.practice-answer-field label,
.practice-choices legend {
  color: var(--color-ink-strong);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.practice-answer-field input,
.practice-math-field {
  width: 100%;
  min-height: var(--control-height);
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-ink-strong);
  padding: 0.7rem 0.8rem;
}

.practice-math-field {
  min-height: 4.5rem;
  font-size: var(--text-xl);
}

.practice-choices label {
  min-height: var(--control-height);
  display: flex;
  gap: var(--space-3);
  align-items: center;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-sm);
  padding: var(--space-3);
}

.practice-choices label:has(input:checked) {
  border-color: var(--brand-action);
  background: var(--brand-action-soft);
}

.practice-feedback {
  margin-block: var(--space-4) 0;
  border-inline-start: 3px solid currentcolor;
  padding-inline-start: var(--space-3);
  color: var(--color-danger);
  font-weight: var(--weight-semibold);
}

.practice-feedback[data-state="correct"] {
  color: var(--color-success);
}

.practice-solution {
  margin-block-start: var(--space-6);
  border-block-start: 1px solid var(--color-line);
  padding-block-start: var(--space-6);
}

.practice-solution details {
  margin-block-start: var(--space-5);
}

.practice-solution summary {
  min-height: var(--control-height);
  display: flex;
  align-items: center;
  color: var(--brand-action-active);
  font-weight: var(--weight-semibold);
  cursor: pointer;
}

.practice-question__actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  margin-block-start: var(--space-5);
}

.practice-complete {
  border: 1px solid var(--color-success-line);
  border-radius: var(--radius-md);
  background: var(--color-success-surface);
  padding: var(--space-6);
  color: var(--color-success);
  font-weight: var(--weight-semibold);
}

.form-status {
  min-height: 1.4rem;
  margin: var(--space-3) 0 0;
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.task-shell[data-live-state="error"] .form-status {
  color: var(--color-danger);
  font-weight: var(--weight-semibold);
}

.task-shell[data-live-state="error"] .result-formula {
  border: 1px solid var(--color-danger-line);
  background: var(--color-danger-surface);
  color: var(--color-danger);
  font-family: var(--font-sans);
  font-size: var(--text-base);
}

.task-shell--focused {
  width: min(100%, 64rem);
  margin-inline: auto;
}

.field-group {
  min-width: 0;
  margin: 0;
  border: 0;
  padding: 0;
}

.field-group + .field-group {
  margin-block-start: var(--space-5);
}

.field-label,
.field-group > legend,
.field > span:first-child {
  color: var(--color-ink-strong);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.field-label-row {
  display: flex;
  justify-content: space-between;
  gap: var(--space-4);
  align-items: end;
  margin-block-end: var(--space-2);
}

.field-hint {
  color: var(--color-text-muted);
  font-size: var(--text-xs);
  text-align: end;
}

.field-label-row > span {
  color: var(--color-text-muted);
  font-size: var(--text-xs);
  text-align: end;
}

.field {
  display: grid;
  gap: var(--space-2);
}

.field input,
.field select,
.field textarea,
.math-field {
  width: 100%;
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-ink);
  padding: 0.62rem 0.75rem;
  transition: border-color var(--duration-fast) var(--ease-out), box-shadow var(--duration-fast) var(--ease-out);
}

.field textarea {
  min-height: 7.5rem;
  resize: vertical;
}

.math-field,
math-field.math-field {
  min-height: 7.5rem;
  display: block;
  padding: var(--space-4);
  font-size: var(--text-2xl);
  line-height: 1.45;
  --caret-color: var(--brand-action-active);
  --selection-background-color: color-mix(in oklch, var(--brand-action) 18%, transparent);
  --contains-highlight-background-color: color-mix(in oklch, var(--brand-action) 10%, transparent);
  --placeholder-color: var(--color-text-faint);
  --smart-fence-color: var(--brand-action-active);
}

.field-error {
  margin-block: var(--space-2) 0;
  color: var(--color-danger);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.segmented-control {
  min-width: 0;
  margin: 0 0 var(--space-5);
  border: 0;
  padding: 0;
}

.segmented-control > legend {
  margin-block-end: var(--space-2);
}

.segmented-control > div {
  display: flex;
  gap: var(--space-2);
  overflow-x: auto;
  overscroll-behavior-inline: contain;
  padding: var(--space-1);
  scrollbar-width: thin;
}

.segmented-control label {
  flex: 0 0 auto;
}

.segmented-control input {
  position: absolute;
  opacity: 0;
  pointer-events: none;
}

.segmented-control label > span {
  min-height: var(--control-height);
  display: inline-flex;
  align-items: center;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-text-muted);
  padding: 0.55rem 0.8rem;
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
  white-space: nowrap;
}

.segmented-control input:checked + span {
  border-color: var(--brand-action);
  background: var(--brand-action-soft);
  color: var(--brand-action-active);
}

.segmented-control input:focus-visible + span {
  outline: 3px solid var(--brand-focus-ring);
  outline-offset: 2px;
}

.math-toolbar,
.example-strip {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  overflow-x: auto;
  overscroll-behavior-inline: contain;
  padding: var(--space-1);
  scrollbar-width: thin;
}

.math-toolbar {
  margin-block-start: var(--space-2);
}

.math-toolbar button,
.example-strip button,
.chip {
  min-width: var(--control-height);
  min-height: var(--control-height);
  flex: 0 0 auto;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-pill);
  background: var(--color-surface);
  color: var(--color-text-muted);
  padding: 0.5rem 0.75rem;
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.math-toolbar button {
  border-radius: var(--radius-sm);
  color: var(--color-ink-strong);
}

.math-toolbar button:hover,
.example-strip button:hover,
.chip:hover,
.chip[aria-pressed="true"],
.chip.is-active {
  border-color: var(--brand-action);
  background: var(--brand-action-soft);
  color: var(--brand-action-active);
}

.context-fields {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-3);
  margin-block-start: var(--space-4);
}

.context-fields label {
  min-width: 0;
  display: grid;
  gap: var(--space-2);
}

.context-fields label > span {
  color: var(--color-ink-strong);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.context-fields input,
.context-fields select {
  width: 100%;
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-ink);
  padding: 0.6rem 0.7rem;
}

.task-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-3);
  margin-block-start: var(--space-5);
}

.task-status {
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-3);
  margin-block-start: var(--space-5);
}

.button-row [role="status"] {
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.page-jumps {
  display: flex;
  gap: var(--space-2);
  overflow-x: auto;
  padding-block: var(--space-4);
  scrollbar-width: none;
}

.page-jumps::-webkit-scrollbar {
  display: none;
}

.page-jumps a {
  min-height: var(--control-height);
  display: inline-flex;
  flex: 0 0 auto;
  align-items: center;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-pill);
  padding-inline: var(--space-3);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  text-decoration: none;
}

.page-jumps a:hover {
  border-color: var(--brand-action);
  color: var(--brand-action-active);
}

.example-row {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin-block-start: var(--space-5);
  overflow-x: auto;
  padding: var(--space-1);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.example-row > * {
  flex: 0 0 auto;
}

.example-row button {
  min-height: var(--control-height);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-pill);
  background: var(--color-surface);
  color: var(--color-text-muted);
  padding: 0.5rem 0.75rem;
}

.example-row button:hover {
  border-color: var(--brand-action);
  background: var(--brand-action-soft);
  color: var(--brand-action-active);
}

.result-panel {
  border-block-start: 1px solid var(--color-line-strong);
  background: var(--color-surface);
  padding: clamp(1.25rem, 3vw, 1.75rem);
}

.result-panel__heading {
  display: flex;
  justify-content: space-between;
  gap: var(--space-4);
  align-items: start;
}

.result-panel__label,
.meta-label {
  margin: 0;
  color: var(--color-success);
  font-size: var(--text-xs);
  font-weight: var(--weight-heavy);
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.result-panel__answer {
  min-height: 6.5rem;
  display: grid;
  align-items: center;
  margin-block-start: var(--space-4);
  border-radius: var(--radius-md);
  background: var(--color-surface-subtle);
  padding: var(--space-4);
  overflow-x: auto;
}

.result-formula,
.question-formula {
  min-height: 6.5rem;
  display: grid;
  align-items: center;
  margin-block-start: var(--space-4);
  border-radius: var(--radius-md);
  background: var(--color-surface-subtle);
  padding: var(--space-4);
  overflow-x: auto;
}

.result-panel__conditions,
.result-conditions,
.interpreted-problem {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: var(--space-3);
  align-items: baseline;
  margin-block-start: var(--space-4);
  border-block: 1px solid var(--color-line);
  padding-block: var(--space-3);
}

.result-conditions p,
.interpreted-problem p {
  margin: 0;
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.result-conditions ul {
  margin: 0;
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.result-panel .section-label {
  color: var(--color-success);
}

.result-panel__plain {
  color: var(--color-text-muted);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  overflow-wrap: anywhere;
}

.step-list {
  display: grid;
  gap: 0;
  margin: var(--space-6) 0 0;
  padding: 0;
  list-style: none;
  counter-reset: step;
}

.step-list > li {
  display: grid;
  grid-template-columns: 2.5rem minmax(0, 1fr);
  gap: var(--space-4);
  border-block-start: 1px solid var(--color-line);
  padding-block: var(--space-5);
  counter-increment: step;
}

.step-list > li::before {
  width: 2.2rem;
  height: 2.2rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--brand-action-soft);
  color: var(--brand-action-active);
  content: counter(step);
  font-size: var(--text-xs);
  font-weight: var(--weight-heavy);
}

.step-list h3,
.step-list p {
  margin: 0;
}

.solution-steps {
  margin-block-start: var(--space-6);
}

.solution-steps ol {
  display: grid;
  gap: 0;
  margin: 0;
  padding: 0;
  list-style: none;
  counter-reset: solution-step;
}

.solution-steps li {
  display: grid;
  grid-template-columns: minmax(12rem, 0.8fr) minmax(0, 1.2fr);
  gap: var(--space-4);
  border-block-start: 1px solid var(--color-line);
  padding-block: var(--space-4);
  counter-increment: solution-step;
}

.solution-steps li::before {
  display: none;
}

.solution-steps li > span:first-child::before {
  margin-inline-end: var(--space-2);
  color: var(--brand-action-active);
  content: counter(solution-step) ".";
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  font-weight: var(--weight-heavy);
}

.verification {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: var(--space-3);
  margin-block-start: var(--space-6);
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-md);
  background: var(--color-surface-subtle);
  padding: var(--space-4);
}

.verification[data-state="success"] {
  border-color: var(--color-success-line);
  background: var(--color-success-surface);
}

.verification > span:first-child {
  width: 1.6rem;
  height: 1.6rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--color-success);
  color: var(--color-surface);
  font-size: var(--text-xs);
  font-weight: var(--weight-heavy);
}

.verification strong,
.verification p {
  margin: 0;
}

.verification p {
  margin-block-start: var(--space-1);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.step-list p {
  margin-block-start: var(--space-1);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.notice {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: var(--space-3);
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-md);
  background: var(--color-surface-subtle);
  padding: var(--space-4);
}

.notice[data-state="success"] {
  border-color: var(--color-success-line);
  background: var(--color-success-surface);
}

.notice[data-state="warning"] {
  border-color: var(--color-warning-line);
  background: var(--color-warning-surface);
}

.notice[data-state="error"] {
  border-color: var(--color-danger-line);
  background: var(--color-danger-surface);
}

.notice__icon {
  width: 1.6rem;
  height: 1.6rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--color-ink);
  color: var(--color-surface);
  font-size: var(--text-xs);
  font-weight: var(--weight-heavy);
}

.notice[data-state="success"] .notice__icon {
  background: var(--color-success);
}

.notice[data-state="warning"] .notice__icon {
  background: var(--color-warning);
}

.notice[data-state="error"] .notice__icon {
  background: var(--color-danger);
}

.notice strong,
.notice p {
  margin: 0;
}

.notice p {
  margin-block-start: var(--space-1);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.formula-stage {
  margin-block: var(--space-6);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-md);
  background: var(--color-surface-subtle);
  padding: clamp(1rem, 3vw, 1.75rem);
}

.formula-stage .katex-display,
.formula-stage .math-display {
  margin-block: 0;
  font-size: var(--text-xl);
}

.formula-stage--parts {
  display: grid;
  gap: var(--space-5);
}

.formula-stage--parts > div + div {
  border-block-start: 1px solid var(--color-line);
  padding-block-start: var(--space-5);
}

.formula-stage--parts strong {
  display: block;
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.article-outline__title {
  color: var(--color-ink-strong);
  font-size: var(--text-xs);
  font-weight: var(--weight-heavy);
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.article-outline > strong {
  color: var(--color-ink-strong);
  font-size: var(--text-xs);
  font-weight: var(--weight-heavy);
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.article-outline nav {
  display: grid;
  gap: var(--space-2);
  margin-block-start: var(--space-3);
}

.article-outline ol {
  display: grid;
  gap: var(--space-2);
  margin: var(--space-3) 0 0;
  padding: 0;
  list-style: none;
}

.article-outline a {
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  line-height: 1.4;
  text-decoration: none;
}

.article-outline ol a {
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  line-height: 1.4;
  text-decoration: none;
}

.article-outline a:hover,
.article-outline a[aria-current="location"] {
  color: var(--brand-action-active);
}

.interactive-lab,
.practice-shell {
  margin-block-start: var(--space-8);
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-lg);
  background: var(--color-surface);
  padding: clamp(1rem, 4vw, 2rem);
  overflow: clip;
}

.interactive-lab > label {
  display: grid;
  gap: var(--space-2);
  margin-block: var(--space-5);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.interactive-lab > label input {
  width: 100%;
}

.range-field {
  display: grid;
  grid-template-columns: auto minmax(8rem, 1fr) 2rem;
  gap: var(--space-3);
  align-items: center;
  margin-block: var(--space-5);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.range-field input {
  width: 100%;
}

.range-field output {
  color: var(--color-ink-strong);
  font-family: var(--font-mono);
  text-align: end;
}

.lab-caption {
  margin-block: var(--space-3) 0;
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.interactive-lab > svg {
  width: 100%;
  min-width: 30rem;
  height: auto;
  overflow: visible;
}

.graph-grid {
  fill: none;
  stroke: var(--color-line);
  stroke-width: 1;
}

.graph-area {
  fill: var(--brand-action-soft);
}

.graph-line {
  fill: none;
  stroke: var(--brand-action-hover);
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-width: 3;
}

.lab-toolbar {
  display: flex;
  gap: var(--space-2);
  overflow-x: auto;
  overscroll-behavior-inline: contain;
  padding: var(--space-1);
}

.range-control {
  display: grid;
  gap: var(--space-3);
  margin-block: var(--space-6);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.range-control input {
  width: 100%;
  min-height: var(--control-height);
}

.data-flow {
  display: grid;
  grid-template-columns: minmax(6rem, 0.7fr) auto minmax(8rem, 1fr) auto minmax(8rem, 1fr);
  gap: var(--space-3);
  align-items: center;
}

.data-flow__node {
  min-width: 0;
  min-height: 6rem;
  display: grid;
  place-content: center;
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  padding: var(--space-3);
  text-align: center;
}

.data-flow__node[data-state="active"] {
  background: var(--brand-action-soft);
}

.data-flow__arrow {
  color: var(--brand-action);
  font-weight: var(--weight-heavy);
}

.graph-frame,
.table-wrap {
  max-width: 100%;
  overflow-x: auto;
  overscroll-behavior-inline: contain;
}

.graph-frame {
  margin-block-start: var(--space-6);
  border-block-start: 1px solid var(--color-line);
  padding-block-start: var(--space-4);
}

.graph-frame svg,
.graph-frame canvas {
  width: 100%;
  min-width: 30rem;
  height: auto;
}

.graph-caption,
.graph-legend {
  color: var(--color-text-muted);
  font-size: var(--text-xs);
}

.graph-legend {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2) var(--space-4);
  margin-block-start: var(--space-2);
}

.graph-legend__item {
  display: inline-flex;
  gap: var(--space-2);
  align-items: center;
}

.graph-legend__swatch {
  width: 1.5rem;
  height: 0;
  border-block-start: 2px solid var(--brand-action-hover);
}

.graph-legend__swatch[data-pattern="dashed"] {
  border-block-start-color: var(--color-ink-strong);
  border-block-start-style: dashed;
}

.resource-list,
.formula-list,
.mistake-list {
  margin: 0;
  border-block-start: 1px solid var(--color-line);
  padding: 0;
  list-style: none;
}

.resource-list > li,
.formula-list > li,
.mistake-list > li,
.mistake-list > article {
  display: grid;
  grid-template-columns: minmax(12rem, 0.75fr) minmax(18rem, 1.25fr);
  gap: clamp(1rem, 4vw, 3rem);
  align-items: baseline;
  border-block-end: 1px solid var(--color-line);
  padding-block: var(--space-5);
}

.resource-list > li {
  position: relative;
}

.resource-list--related > li {
  grid-template-columns: minmax(0, 1fr) auto;
  align-items: center;
}

.resource-list--related > li > div {
  width: 100%;
  max-width: none;
}

.resource-list > li.resource-list__content-only {
  grid-template-columns: minmax(0, 1fr);
}

.resource-list__content-only > div {
  max-width: 72ch;
}

.resource-list > li h3 a::after {
  position: absolute;
  content: "";
  inset: 0;
}

.resource-list--numbered > li {
  grid-template-columns: 2.5rem minmax(0, 1fr) auto;
  align-items: center;
}

.resource-number {
  color: var(--brand-action-active);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  font-weight: var(--weight-heavy);
}

.resource-list h3,
.resource-list p,
.formula-list h3,
.formula-list p,
.mistake-list h3,
.mistake-list p {
  margin: 0;
}

.site-footer__inner > div > p {
  max-width: 34rem;
  margin-block-start: var(--space-3);
  color: var(--color-text-muted);
}

.site-footer__inner > nav {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: var(--space-2) var(--space-4);
  align-content: start;
}

.site-footer__inner > nav a {
  min-height: var(--control-height);
  display: flex;
  align-items: center;
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.resource-list p,
.formula-list p,
.mistake-list p {
  color: var(--color-text-muted);
}

.practice-header {
  display: flex;
  justify-content: space-between;
  gap: var(--space-5);
  align-items: start;
  border-block-end: 1px solid var(--color-line);
  padding-block-end: var(--space-5);
}

.practice-progress {
  min-width: 10rem;
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.practice-progress progress {
  width: 100%;
  height: 0.55rem;
  display: block;
  margin-block-start: var(--space-2);
  accent-color: var(--brand-action);
}

.practice-question {
  padding-block: var(--space-8);
}

.practice-question__prompt {
  color: var(--color-ink-strong);
  font-size: var(--text-xl);
  font-weight: var(--weight-semibold);
}

.choice-list {
  display: grid;
  gap: var(--space-2);
  margin: var(--space-5) 0 0;
  padding: 0;
  list-style: none;
}

.choice-list label {
  min-height: var(--control-height);
  display: flex;
  gap: var(--space-3);
  align-items: center;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  padding: 0.65rem 0.8rem;
}

.choice-list label:hover,
.choice-list label:has(input:checked) {
  border-color: var(--brand-action);
  background: var(--brand-action-soft);
}

.method-choice {
  margin: 0;
  border: 0;
  padding: 0;
}

.method-choice legend {
  color: var(--color-ink-strong);
  font-weight: var(--weight-semibold);
}

.method-choice .choice-list {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.practice-feedback,
.empty-state {
  margin-block-start: var(--space-5);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-md);
  background: var(--color-surface-subtle);
  padding: var(--space-5);
}

.practice-feedback[data-state="correct"] {
  border-color: var(--color-success-line);
  background: var(--color-success-surface);
}

.practice-feedback[data-state="incorrect"] {
  border-color: var(--color-danger-line);
  background: var(--color-danger-surface);
}

.practice-score {
  border-block-start: 1px solid var(--color-line);
  padding-block-start: var(--space-6);
}

.practice-paths {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: var(--space-4);
  max-width: 52rem;
  margin-block-end: var(--space-12);
}

.practice-paths article {
  position: relative;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  padding: var(--space-5);
}

.practice-paths article > a {
  min-height: var(--control-height);
  display: inline-flex;
  align-items: center;
  margin-block-start: var(--space-3);
  font-weight: var(--weight-semibold);
}

.practice-paths article > a::after {
  position: absolute;
  content: "";
  inset: 0;
}

.practice-paths article:first-child {
  border-color: var(--brand-action);
  background: var(--brand-action-soft);
}

.practice-paths h3,
.practice-paths p {
  margin: 0;
}

.practice-paths p + h3,
.practice-paths h3 + p {
  margin-block-start: var(--space-2);
}

.practice-paths article > span:last-child {
  display: block;
  margin-block-start: var(--space-4);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.practice-start {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: var(--space-8);
  align-items: end;
  border-block: 1px solid var(--color-line);
  padding-block: var(--space-6);
}

.practice-start > div:first-child {
  max-width: 48rem;
}

.practice-start h2,
.practice-start p,
.practice-start dl {
  margin-block-end: 0;
}

.practice-start--test {
  grid-template-columns: minmax(0, 1fr) minmax(15rem, 0.45fr) auto;
}

.practice-start dl {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-4);
}

.practice-start dt {
  color: var(--color-text-muted);
  font-size: var(--text-xs);
  font-weight: var(--weight-semibold);
}

.practice-start dd {
  margin: var(--space-1) 0 0;
  color: var(--color-ink-strong);
  font-weight: var(--weight-bold);
}

.practice-progress > div {
  display: flex;
  justify-content: space-between;
  gap: var(--space-4);
}

.question-panel {
  padding-block-start: var(--space-8);
}

.question-panel form {
  display: grid;
  gap: var(--space-2);
  margin-block-start: var(--space-6);
}

.question-panel form > label,
.search-field > span {
  color: var(--color-ink-strong);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.question-panel input,
.search-field input {
  width: 100%;
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-ink);
  padding: 0.62rem 0.75rem;
}

.answer-feedback {
  min-height: 1.5rem;
  margin: var(--space-2) 0 0;
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.question-nav {
  display: flex;
  justify-content: space-between;
  gap: var(--space-3);
  border-block-start: 1px solid var(--color-line);
  padding-block-start: var(--space-5);
}

.test-brief {
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(18rem, 0.65fr);
  gap: clamp(2rem, 6vw, 5rem);
  align-items: end;
  border-block-end: 1px solid var(--color-line);
  padding-block-end: var(--space-8);
}

.test-brief h2,
.test-brief p {
  margin-block-end: 0;
}

.test-brief dl {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-4);
  margin: 0;
}

.test-brief dl > div {
  min-width: 0;
}

.test-brief dt {
  color: var(--color-text-muted);
  font-size: var(--text-xs);
}

.test-brief dd {
  margin: var(--space-1) 0 0;
  color: var(--color-ink-strong);
  font-weight: var(--weight-semibold);
}

.locked-solution {
  margin-block-start: var(--space-8);
  border-block: 1px solid var(--color-line);
  padding-block: var(--space-4);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.locked-solution span {
  display: inline-block;
  margin-inline-end: var(--space-2);
  color: var(--brand-action);
}

.test-question-index {
  display: flex;
  gap: var(--space-5);
  align-items: center;
  border-block-start: 1px solid var(--color-line);
  padding-block: var(--space-5);
}

.test-question-index > span {
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.test-question-index ol {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin: 0;
  padding: 0;
  list-style: none;
}

.test-question-index button {
  width: var(--control-height);
  min-height: var(--control-height);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-ink);
  font: inherit;
}

.test-question-index button:hover {
  border-color: var(--brand-action);
}

.test-question-index button[aria-current] {
  border-color: var(--brand-action);
  background: var(--brand-action-soft);
  color: var(--brand-action-active);
  font-weight: var(--weight-semibold);
}

.test-review-sample {
  margin-block-start: var(--space-12);
  border-block-start: 1px solid var(--color-line);
  padding-block-start: var(--space-8);
}

.test-review-sample h2 {
  margin-block-start: var(--space-2);
}

.score-line {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: var(--space-5);
  align-items: baseline;
}

.score-line strong {
  color: var(--color-ink-strong);
  font-size: var(--text-2xl);
}

.score-line p {
  margin: 0;
  color: var(--color-text-muted);
}

.test-review-sample ul {
  margin-block-start: var(--space-6);
  border-block-start: 1px solid var(--color-line);
  padding: 0;
  list-style: none;
}

.test-review-sample li {
  display: flex;
  justify-content: space-between;
  gap: var(--space-4);
  border-block-end: 1px solid var(--color-line);
  padding-block: var(--space-4);
}

.test-review-sample li span {
  color: var(--color-text-muted);
}

.formula-index {
  display: grid;
  grid-template-columns: minmax(12rem, 0.35fr) minmax(0, 1fr);
  gap: clamp(2rem, 6vw, 5rem);
  align-items: start;
}

.formula-index__nav {
  position: sticky;
  inset-block-start: var(--space-6);
}

.formula-topic-nav {
  display: grid;
  gap: var(--space-1);
  margin-block-start: var(--space-6);
  border-block-start: 1px solid var(--color-line);
  padding-block-start: var(--space-3);
}

.formula-topic-nav a {
  min-height: var(--control-height);
  display: flex;
  align-items: center;
  border-block-end: 1px solid var(--color-line);
  color: var(--color-text-muted);
}

.formula-topic-nav a:hover {
  color: var(--brand-action-active);
}

.formula-actions {
  display: flex;
  justify-content: space-between;
  gap: var(--space-8);
  align-items: end;
  border-block: 1px solid var(--color-line);
}

.formula-actions > div:first-child {
  max-width: 48rem;
}

.formula-actions h2,
.formula-actions p {
  margin-block-end: 0;
}

.formula-actions .button-row {
  flex: 0 0 auto;
  margin: 0;
}

.content-grid {
  display: grid;
  gap: var(--space-6);
}

.content-grid--two {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.content-grid > article {
  padding-block-start: 0;
}

.content-grid article p:last-child,
.content-grid article ul:last-child {
  margin-block-end: 0;
}

.capability-examples {
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  line-height: 1.55;
}

.capability-examples strong {
  color: var(--color-text);
  font-weight: var(--weight-semibold);
}

.example-catalog {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-5);
}

.example-catalog article {
  min-width: 0;
  border-block-start: 1px solid var(--color-line);
  padding-block-start: var(--space-5);
}

.example-catalog__header h3,
.example-catalog__header h4 {
  margin: 0 0 var(--space-2);
  font-size: var(--text-lg);
  line-height: 1.3;
}

.example-catalog__header p {
  max-width: 42ch;
  margin: 0;
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  line-height: 1.55;
}

.example-catalog__math {
  min-height: 5.5rem;
  display: grid;
  align-items: center;
  margin-block: var(--space-4);
  overflow-x: auto;
}

.example-catalog__result {
  border-block-start: 1px solid var(--color-line);
  padding-block-start: var(--space-3);
}

.example-catalog__result > p {
  margin: 0 0 var(--space-2);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.example-groups {
  display: grid;
  gap: var(--space-10);
}

.example-group + .example-group {
  border-block-start: 1px solid var(--color-line);
  padding-block-start: var(--space-8);
}

.example-group > h3 {
  margin: 0 0 var(--space-5);
  color: var(--color-ink-strong);
  font-size: var(--text-xl);
}

.example-catalog--group {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.example-catalog--group article {
  border-block-start: 0;
  padding-block-start: 0;
}

.example-group__more {
  margin-block-start: var(--space-5);
  border-block-start: 1px solid var(--color-line);
  padding-block-start: var(--space-3);
}

.example-group__more > summary {
  min-height: var(--control-height);
  display: inline-flex;
  align-items: center;
  color: var(--brand-action-active);
  cursor: pointer;
  font-weight: var(--weight-semibold);
}

.example-group__more[open] > summary {
  margin-block-end: var(--space-5);
}

.example-catalog__result > div {
  overflow-x: auto;
}

.mistake-guide {
  border-block-start: 1px solid var(--color-line);
}

.mistake-guide article {
  display: grid;
  grid-template-columns: minmax(12rem, 0.55fr) minmax(0, 1fr);
  gap: var(--space-3) clamp(2rem, 6vw, 5rem);
  border-block-end: 1px solid var(--color-line);
  padding-block: var(--space-5);
}

.mistake-guide article h3 {
  grid-row: 1 / span 3;
}

.mistake-guide article p {
  margin: 0;
}

.guide-prerequisites {
  margin-block: var(--space-6);
  border-block: 1px solid var(--color-line);
  background: var(--color-surface);
  padding-block: var(--space-4);
}

.guide-prerequisites p {
  margin: var(--space-1) 0 0;
  color: var(--color-text-muted);
}

.worked-example-series article + article {
  margin-block-start: var(--space-12);
  border-block-start: 1px solid var(--color-line-strong);
  padding-block-start: var(--space-10);
}

.worked-example-series article > ol > li + li {
  margin-block-start: var(--space-4);
}

.table-scroll {
  max-width: 100%;
  overflow-x: auto;
}

.symbol-table {
  width: 100%;
  min-width: 38rem;
}

.symbol-table th,
.symbol-table td {
  border-block-end: 1px solid var(--color-line);
  padding: var(--space-4);
  vertical-align: top;
}

.symbol-table th {
  color: var(--color-text-muted);
  font-size: var(--text-xs);
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.publisher-note {
  border-block-start: 1px solid var(--color-line);
  padding-block: var(--space-6) var(--space-12);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
}

.publisher-note p {
  max-width: 72ch;
  margin: 0;
}

.formula-table {
  width: 100%;
  min-width: 36rem;
  text-align: start;
}

.formula-table th,
.formula-table td {
  border-block-end: 1px solid var(--color-line);
  padding: 0.85rem;
  vertical-align: top;
}

.formula-table th {
  color: var(--color-text-muted);
  font-size: var(--text-xs);
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.formula-index__tools {
  position: sticky;
  inset-block-start: var(--space-6);
}

.formula-search-status {
  display: flex;
  justify-content: space-between;
  gap: var(--space-3);
  align-items: center;
  margin-block-start: var(--space-2);
  color: var(--color-text-muted);
  font-size: var(--text-xs);
}

.formula-utility-actions {
  display: grid;
  gap: var(--space-2);
  margin-block-start: var(--space-6);
}

.formula-source-note {
  margin-block: var(--space-2) 0;
  color: var(--color-text-muted);
  font-size: var(--text-xs);
}

.search-field {
  display: grid;
  gap: var(--space-2);
}

.formula-groups {
  min-width: 0;
}

.formula-groups > section + section {
  margin-block-start: var(--space-10);
}

.formula-list > div {
  display: grid;
  grid-template-columns: minmax(15rem, 0.9fr) minmax(14rem, 1.1fr);
  gap: clamp(1rem, 4vw, 3rem);
  align-items: center;
  border-block-end: 1px solid var(--color-line);
  padding-block: var(--space-5);
}

.formula-list dt,
.formula-list dd {
  min-width: 0;
  margin: 0;
}

.formula-list dt .katex-display {
  scrollbar-width: thin;
}

.katex-display.has-horizontal-overflow {
  border-inline-end: 3px solid var(--brand-action-soft);
  scrollbar-color: var(--brand-action) var(--color-surface-subtle);
  scrollbar-width: thin;
}

.formula-list dd {
  display: grid;
  gap: var(--space-1);
  color: var(--color-text-muted);
}

.formula-list dd strong {
  color: var(--color-ink-strong);
}

.disclosure-list {
  width: 100%;
  border-block-start: 1px solid var(--color-line);
}

.disclosure-list details {
  border-block-end: 1px solid var(--color-line);
}

.disclosure-list summary {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
  color: var(--color-ink-strong);
  font-weight: var(--weight-semibold);
  list-style: none;
}

.disclosure-list summary::-webkit-details-marker {
  display: none;
}

.disclosure-list summary::after {
  flex: 0 0 auto;
  color: var(--brand-action);
  content: "+";
  font-size: var(--text-xl);
}

.disclosure-list details[open] summary::after {
  content: "−";
}

.disclosure-list details > :not(summary) {
  max-width: none;
  padding: 0 clamp(2.5rem, 6vw, 6rem) var(--space-4) 0;
  color: var(--color-text-muted);
}

.answer-disclosure {
  border-block: 1px solid var(--color-line);
}

.answer-disclosure summary {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
  color: var(--color-ink-strong);
  font-weight: var(--weight-semibold);
  list-style: none;
}

.answer-disclosure summary::-webkit-details-marker {
  display: none;
}

.answer-disclosure summary::after {
  color: var(--brand-action);
  content: "+";
  font-size: var(--text-xl);
}

.answer-disclosure[open] summary::after {
  content: "−";
}

.answer-disclosure > div {
  padding-block-end: var(--space-4);
  color: var(--color-text-muted);
}

.worked-steps {
  margin: var(--space-6) 0 0;
  padding: 0;
  list-style: none;
}

.worked-steps > li {
  display: grid;
  grid-template-columns: 2.5rem minmax(0, 1fr);
  gap: var(--space-4);
  border-block-start: 1px solid var(--color-line);
  padding-block: var(--space-5);
}

.worked-steps > li > span {
  width: 2.2rem;
  height: 2.2rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--brand-action-soft);
  color: var(--brand-action-active);
  font-weight: var(--weight-heavy);
}

.worked-steps strong,
.worked-steps p {
  margin: 0;
}

.worked-steps p {
  margin-block-start: var(--space-1);
  color: var(--color-text-muted);
}

.hub-primary {
  padding-block-start: var(--space-6);
}

.hub-task-list {
  max-width: 68rem;
  margin: 0;
  padding: 0;
  list-style: none;
}

.hub-task-list > li {
  border-block-end: 1px solid var(--color-line);
}

.hub-task-list > li:not(.hub-task-list__primary):first-of-type {
  border-block-start: 1px solid var(--color-line);
}

.hub-task-list > li > a {
  min-height: 7.25rem;
  display: grid;
  grid-template-columns: 2.5rem minmax(0, 1fr) auto;
  gap: var(--space-5);
  align-items: center;
  color: var(--color-ink-strong);
  padding: var(--space-5) var(--space-4);
  text-decoration: none;
}

.hub-task-list__primary {
  margin-block-end: var(--space-4);
  border: 1px solid color-mix(in oklch, var(--brand-action) 38%, var(--color-line));
  border-radius: var(--radius-md);
  background: var(--brand-action-soft);
}

.hub-task-list__number {
  width: 2.35rem;
  height: 2.35rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--color-surface-selected);
  color: var(--brand-action-active);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  font-weight: var(--weight-heavy);
}

.hub-task-list__primary .hub-task-list__number {
  background: var(--brand-action-hover);
  color: var(--brand-on-action);
}

.hub-task-list__copy {
  min-width: 0;
  display: grid;
  gap: var(--space-1);
}

.hub-task-list__copy small {
  color: var(--brand-action-active);
  font-size: var(--text-sm);
  font-weight: var(--weight-semibold);
}

.hub-task-list__copy strong {
  font-size: var(--text-xl);
  line-height: var(--leading-heading);
}

.hub-task-list__copy > span:last-child {
  max-width: 65ch;
  color: var(--color-text-muted);
  line-height: 1.55;
}

.hub-task-list__arrow {
  color: var(--brand-action);
  font-size: var(--text-2xl);
  transition: transform var(--duration-fast) var(--ease-out);
}

.hub-task-list a:hover .hub-task-list__copy strong {
  color: var(--brand-action-active);
}

.hub-task-list a:hover .hub-task-list__arrow {
  transform: translateX(0.2rem);
}

.hub-context {
  max-width: 68ch;
  margin: var(--space-8) 0 0;
  color: var(--color-text-muted);
}

.hub-concept-grid > article:last-child:nth-child(odd) {
  grid-column: 1 / -1;
  max-width: 48rem;
}

.hub-lead {
  min-height: 6rem;
  display: flex;
  justify-content: space-between;
  gap: var(--space-5);
  align-items: center;
  border-block: 1px solid var(--color-line-strong);
  color: var(--color-ink-strong);
  padding-block: var(--space-5);
  text-decoration: none;
}

.hub-lead span:first-child {
  display: grid;
  gap: var(--space-1);
}

.hub-lead small {
  color: var(--color-text-muted);
}

.hub-lead strong {
  font-size: var(--text-2xl);
}

.hub-lead > span:last-child {
  color: var(--brand-action);
  font-size: var(--text-3xl);
}

.hub-groups {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: clamp(2rem, 7vw, 6rem);
  margin-block-start: var(--space-12);
}

.hub-groups h2 {
  font-size: var(--text-2xl);
}

.hub-groups ul,
.inline-link-list {
  margin: 0;
  border-block-start: 1px solid var(--color-line);
  padding: 0;
  list-style: none;
}

.hub-groups li,
.inline-link-list li {
  border-block-end: 1px solid var(--color-line);
}

.hub-groups a,
.inline-link-list a {
  min-height: var(--control-height);
  display: flex;
  justify-content: space-between;
  gap: var(--space-4);
  align-items: center;
  color: var(--color-ink-strong);
  padding-block: var(--space-4);
  font-weight: var(--weight-semibold);
  text-decoration: none;
}

.hub-groups a:hover,
.inline-link-list a:hover {
  color: var(--brand-action-active);
}

.hub-groups a span {
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  text-align: end;
}

.preview-return {
  border-block-start: 1px solid var(--color-line);
  padding-block: var(--space-8) var(--space-16);
}

.loading-placeholder {
  min-height: 1em;
  border-radius: var(--radius-sm);
  background: linear-gradient(100deg, var(--color-surface-subtle) 25%, var(--color-surface-selected) 45%, var(--color-surface-subtle) 65%);
  background-size: 200% 100%;
  animation: loading-sweep 1.2s linear infinite;
}

@keyframes loading-sweep {
  to {
    background-position-x: -200%;
  }
}

@media (max-width: 51.25rem) {
  .practice-start,
  .practice-start--test {
    grid-template-columns: minmax(0, 1fr);
    align-items: start;
    gap: var(--space-5);
  }

  .practice-start .button {
    justify-self: start;
  }

  .nav-menu {
    display: block;
  }

  .primary-nav {
    display: none;
  }

  .mobile-nav {
    display: block;
  }

  .article-outline {
    border-block: 1px solid var(--color-line);
    padding-block: var(--space-4);
  }

  .article-outline nav {
    display: flex;
    overflow-x: auto;
    padding-block: var(--space-1);
  }

  .article-outline ol {
    display: flex;
    flex-wrap: wrap;
    overflow-x: visible;
    gap: var(--space-2);
    padding-block: var(--space-1);
  }

  .article-outline a {
    min-height: var(--control-height);
    display: inline-flex;
    flex: 0 0 auto;
    align-items: center;
    border: 1px solid var(--color-line);
    border-radius: var(--radius-pill);
    padding-inline: var(--space-3);
  }

  .article-outline ol a {
    min-height: var(--control-height);
    display: inline-flex;
    flex: 0 0 auto;
    align-items: center;
    border: 1px solid var(--color-line);
    border-radius: var(--radius-pill);
    padding-inline: var(--space-3);
  }

  .article-outline ol li {
    display: flex;
  }

  .formula-index {
    grid-template-columns: minmax(0, 1fr);
  }

  .formula-index__nav {
    position: static;
  }

  .formula-index__tools {
    position: static;
  }

  .formula-actions {
    align-items: flex-start;
    flex-direction: column;
    gap: var(--space-5);
  }

  .formula-actions .button-row {
    width: 100%;
  }

  .example-catalog {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 40.625rem) {
  .practice-set__header {
    grid-template-columns: minmax(0, 1fr);
    gap: var(--space-4);
  }

  .practice-progress {
    min-width: 0;
  }

  .field-label-row,
  .practice-header {
    align-items: flex-start;
    flex-direction: column;
  }

  .field-hint {
    text-align: start;
  }

  .context-fields {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .result-panel__heading {
    align-items: center;
  }

  .result-panel__conditions,
  .result-conditions,
  .interpreted-problem,
  .resource-list > li,
  .formula-list > li,
  .mistake-list > li,
  .mistake-list > article {
    grid-template-columns: minmax(0, 1fr);
    gap: var(--space-2);
  }

  .resource-list--related > li {
    grid-template-columns: minmax(0, 1fr) auto;
    align-items: center;
  }

  .solution-steps li,
  .formula-list > div {
    grid-template-columns: minmax(0, 1fr);
    gap: var(--space-2);
  }

  .data-flow {
    grid-template-columns: minmax(0, 1fr);
  }

  .data-flow__arrow {
    justify-self: center;
    transform: rotate(90deg);
  }

  .task-actions .button {
    flex: 1 1 8rem;
  }

  .practice-paths,
  .hub-groups,
  .content-grid--two,
  .example-catalog,
  .mistake-guide article {
    grid-template-columns: minmax(0, 1fr);
  }

  .mistake-guide article h3 {
    grid-row: auto;
  }

  .hub-task-list > li > a {
    grid-template-columns: 2.35rem minmax(0, 1fr);
    gap: var(--space-3);
    padding-inline: var(--space-3);
  }

  .hub-task-list__arrow {
    display: none;
  }

  .hub-concept-grid > article:last-child:nth-child(odd) {
    grid-column: auto;
  }

  .method-choice .choice-list,
  .test-brief,
  .score-line {
    grid-template-columns: minmax(0, 1fr);
  }

  .test-brief {
    gap: var(--space-6);
  }

  .test-brief dl {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

  .test-question-index {
    align-items: flex-start;
    flex-direction: column;
  }

  .test-review-sample li {
    align-items: flex-start;
    flex-direction: column;
    gap: var(--space-1);
  }


  .site-footer__inner > nav {
    grid-template-columns: minmax(0, 1fr);
  }

  .interactive-lab {
    overflow-x: auto;
  }

  .symbol-table {
    min-width: 0;
  }

  .symbol-table thead {
    display: none;
  }

  .symbol-table tbody,
  .symbol-table tr,
  .symbol-table td {
    display: block;
    width: 100%;
  }

  .symbol-table tr {
    border-block-end: 1px solid var(--color-line);
    padding-block: var(--space-4);
  }

  .symbol-table td {
    display: grid;
    grid-template-columns: 5rem minmax(0, 1fr);
    gap: var(--space-3);
    border: 0;
    padding: var(--space-1) 0;
  }

  .symbol-table td::before {
    color: var(--color-text-muted);
    content: attr(data-label);
    font-size: var(--text-xs);
    font-weight: var(--weight-semibold);
    letter-spacing: 0.04em;
    text-transform: uppercase;
  }
}

@media (max-width: 30rem) {
  .page-intro--task {
    padding-block-top: var(--space-6);
    padding-block-end: var(--space-3);
  }

  .page-intro--task .direct-answer {
    display: none;
  }

  .page-intro--task .lede {
    font-size: var(--text-base);
  }

  .section-heading--primary-choice {
    margin-block-end: var(--space-4);
  }

  .section-heading--primary-choice > p:not(.section-label) {
    display: none;
  }

  .hub-primary,
  .practice-primary {
    padding-block-start: 0;
  }

  .hub-groups {
    margin-block-start: var(--space-8);
  }

  .practice-paths {
    margin-block-end: var(--space-6);
  }

  .field-label-row > span {
    display: none;
  }

  .task-shell .solver-form textarea {
    min-height: 5.75rem;
  }

  .formula-actions .button {
    flex: 1 1 100%;
  }
  .result-panel__heading {
    align-items: stretch;
    flex-direction: column;
  }

  .disclosure-list details > :not(summary) {
    padding-inline-end: var(--space-6);
  }

  .brand-lockup__wide {
    display: none;
  }

  .brand-lockup__mark {
    display: block;
  }

  .resource-list--numbered > li {
    grid-template-columns: 2rem minmax(0, 1fr);
  }

  .resource-list--numbered > li > :last-child {
    display: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  .loading-placeholder {
    animation: none;
  }
}

}
@layer utilities {
.sr-only {
  position: absolute !important;
  width: 1px !important;
  height: 1px !important;
  margin: -1px !important;
  overflow: hidden !important;
  clip: rect(0, 0, 0, 0) !important;
  clip-path: inset(50%) !important;
  white-space: nowrap !important;
}

.measure {
  max-width: 72ch;
}

.measure--compact {
  max-width: 60ch;
}

.text-muted {
  color: var(--color-text-muted);
}

.text-danger {
  color: var(--color-danger);
}

.text-success {
  color: var(--color-success);
}

.surface-subtle {
  background: var(--color-surface-subtle);
}

.border-block {
  border-block: 1px solid var(--color-line);
}

.scroll-inline {
  max-width: 100%;
  overflow-x: auto;
  overflow-y: hidden;
  overscroll-behavior-inline: contain;
}

.full-width {
  width: 100%;
}

.no-wrap {
  white-space: nowrap;
}

.break-anywhere {
  overflow-wrap: anywhere;
}

.push-inline-end {
  margin-inline-start: auto;
}

.flow > * {
  margin-block: 0;
}

.flow > * + * {
  margin-block-start: var(--flow-space, var(--space-4));
}

.only-wide {
  display: initial;
}

.only-narrow {
  display: none;
}

@media (max-width: 51.25rem) {
  .only-wide {
    display: none !important;
  }

  .only-narrow {
    display: initial;
  }
}

}