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

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-width: 20rem;
  background: var(--color-canvas);
  color: var(--color-ink);
  font-family: var(--font-body);
  font-size: var(--text-body);
  line-height: 1.6;
  letter-spacing: -0.02em;
  text-rendering: optimizeLegibility;
}

a {
  color: var(--color-primary);
  -webkit-tap-highlight-color: transparent;
}

:focus-visible {
  outline: 2px solid var(--color-primary-focus);
  outline-offset: 3px;
  box-shadow: 0 0 0 4px var(--color-focus-halo);
}

.skip-link {
  position: fixed;
  top: var(--space-sm);
  left: var(--space-sm);
  z-index: 100;
  padding: var(--space-sm) var(--space-md);
  border-radius: var(--radius-sm);
  background: var(--color-canvas);
  transform: translateY(-200%);
}

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

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  border-bottom: 1px solid var(--color-hairline);
  background: var(--color-frosted);
  backdrop-filter: saturate(180%) blur(20px);
}

.header-inner {
  width: min(100% - 2rem, var(--content-wide));
  min-height: var(--nav-height);
  display: flex;
  align-items: center;
  gap: var(--space-lg);
  margin: 0 auto;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
  color: var(--color-ink);
  font-size: var(--text-caption);
  font-weight: 600;
  text-decoration: none;
  white-space: nowrap;
}

.brand-mark {
  width: 2rem;
  height: 2rem;
  display: grid;
  place-items: center;
  border-radius: var(--radius-sm);
  background: var(--color-ink);
  color: var(--color-canvas);
  font-size: var(--text-fine);
}

.header-nav {
  display: flex;
  gap: var(--space-lg);
  margin-left: auto;
}

.header-nav a,
.course-link {
  color: var(--color-ink-soft);
  font-size: var(--text-caption);
  text-decoration: none;
  white-space: nowrap;
}

.header-nav a:hover,
.course-link:hover {
  color: var(--color-primary);
}

.course-link {
  padding-left: var(--space-lg);
  border-left: 1px solid var(--color-hairline);
}

.hero {
  background: var(--color-canvas-parchment);
}

.hero-inner {
  width: min(100% - 2rem, 70rem);
  margin: 0 auto;
  padding: clamp(4.5rem, 10vw, 8rem) 0 clamp(4rem, 8vw, 6rem);
  text-align: center;
}

.eyebrow {
  margin: 0 0 var(--space-sm);
  color: var(--color-primary);
  font-size: var(--text-fine);
  font-weight: 600;
  letter-spacing: 0.08em;
}

.hero h1 {
  max-width: 15ch;
  margin: 0 auto;
  font-family: var(--font-display);
  font-size: var(--text-hero);
  font-weight: 600;
  line-height: 1.08;
  letter-spacing: -0.035em;
  word-break: keep-all;
}

.hero-copy {
  max-width: 42rem;
  margin: var(--space-lg) auto 0;
  color: var(--color-ink-soft);
  font-family: var(--font-display);
  font-size: var(--text-lead);
  line-height: 1.55;
  word-break: keep-all;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: var(--space-sm);
  margin-top: var(--space-xl);
}

.button {
  min-height: 2.75rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid transparent;
  border-radius: var(--radius-pill);
  padding: 0.65rem 1.35rem;
  font-size: var(--text-caption);
  text-decoration: none;
}

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

.button-secondary {
  border-color: var(--color-primary);
  background: transparent;
}

.map,
.lesson,
.summary {
  width: min(100% - 2rem, 70rem);
  margin-inline: auto;
}

.map {
  padding: var(--space-section) 0;
}

.section-heading {
  max-width: 44rem;
}

.section-heading h2,
.chapter-header h2,
.summary h2 {
  margin: 0;
  font-family: var(--font-display);
  font-size: var(--text-section);
  line-height: 1.16;
  letter-spacing: -0.025em;
  word-break: keep-all;
}

.section-heading > p:last-child,
.chapter-header > p:last-child {
  color: var(--color-ink-soft);
}

.map-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: var(--space-sm);
  margin: var(--space-xl) 0 0;
  padding: 0;
  list-style: none;
}

.map-grid a {
  min-width: 0;
  min-height: 8rem;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  gap: var(--space-lg);
  padding: var(--space-lg);
  border-radius: var(--radius-lg);
  background: var(--color-canvas-parchment);
  color: var(--color-ink);
  text-decoration: none;
}

.map-grid a:hover {
  color: var(--color-primary);
}

.map-grid strong {
  color: var(--color-primary);
  font-size: var(--text-fine);
}

.map-grid span {
  font-weight: 600;
  overflow-wrap: anywhere;
  word-break: keep-all;
}

.map-grid > li {
  min-width: 0;
}

.fiction-banner {
  margin: var(--space-xl) 0 0;
  padding: var(--space-md) var(--space-lg);
  border-left: 3px solid var(--color-primary);
  border-radius: var(--radius-md);
  background: var(--color-canvas-parchment);
  color: var(--color-ink-soft);
  font-size: var(--text-caption);
}

.chapter {
  scroll-margin-top: calc(var(--nav-height) + var(--space-lg));
  padding: var(--space-section) 0;
  border-top: 1px solid var(--color-hairline);
}

.chapter-header {
  max-width: 48rem;
  margin-bottom: var(--space-xxl);
}

.chapter-header > p:last-child {
  margin-top: var(--space-lg);
  font-size: var(--text-lead);
  line-height: 1.5;
}

.concept-card,
.metric-card,
.three-step section,
.comparison-grid section {
  border: 1px solid var(--color-hairline);
  border-radius: var(--radius-lg);
  padding: clamp(1.25rem, 3vw, 2rem);
  background: var(--color-canvas);
}

.concept-card h3,
.metric-card h3,
.worked-example h3,
.learn-more h3,
.three-step h3,
.comparison-grid h3,
.safety h3,
.callout h3 {
  margin: 0;
  font-family: var(--font-display);
  line-height: 1.25;
}

.table-wrap {
  overflow-x: auto;
  margin-top: var(--space-lg);
}

table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
}

caption {
  padding-bottom: var(--space-sm);
  color: var(--color-ink-muted);
  font-size: var(--text-caption);
  text-align: left;
}

th,
td {
  min-width: 9rem;
  padding: var(--space-md);
  border: 1px solid var(--color-hairline);
  vertical-align: top;
}

thead th {
  background: var(--color-canvas-parchment);
}

.metric-grid,
.split-grid,
.comparison-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: var(--space-lg);
  margin-top: var(--space-lg);
}

.metric-kicker,
.tag {
  margin: 0 0 var(--space-xs);
  color: var(--color-primary);
  font-size: var(--text-fine);
  font-weight: 600;
}

.formula {
  overflow-wrap: anywhere;
  margin: var(--space-lg) 0;
  padding: var(--space-md);
  border-radius: var(--radius-md);
  background: var(--color-canvas-parchment);
  font-family: ui-monospace, "SFMono-Regular", Consolas, monospace;
  font-weight: 600;
  letter-spacing: -0.02em;
}

.worked-example {
  margin-top: var(--space-xxl);
  padding: clamp(1.5rem, 4vw, 3rem);
  border-radius: var(--radius-lg);
  background: var(--color-dark);
  color: var(--color-canvas);
}

.worked-example > p {
  color: var(--color-dark-muted);
}

.calculation-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: var(--space-sm);
  margin: var(--space-xl) 0;
  padding: 0;
  list-style: none;
}

.calculation-list li {
  display: flex;
  flex-direction: column;
  gap: var(--space-xs);
  padding: var(--space-md);
  border-radius: var(--radius-md);
  background: rgba(255, 255, 255, 0.08);
}

.calculation-list strong {
  color: var(--color-primary-on-dark);
  font-size: var(--text-caption);
}

.takeaway {
  margin-bottom: 0;
  padding-top: var(--space-lg);
  border-top: 1px solid rgba(255, 255, 255, 0.2);
}

.fiction-note {
  margin-bottom: 0;
  color: var(--color-dark-muted);
  font-size: var(--text-fine);
}

.resource-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xxs);
  margin-top: var(--space-md);
  font-size: var(--text-caption);
  font-weight: 600;
  line-height: 1.4;
  text-decoration: none;
}

.learn-more {
  display: grid;
  grid-template-columns: 1fr 1.4fr auto;
  align-items: center;
  gap: var(--space-lg);
  margin-top: var(--space-xxl);
  padding: var(--space-lg);
  border-top: 1px solid var(--color-hairline);
  border-bottom: 1px solid var(--color-hairline);
}

.learn-more p {
  color: var(--color-ink-soft);
}

.learn-more a {
  white-space: nowrap;
  text-decoration: none;
}

.three-step {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-lg);
}

.three-step span {
  display: block;
  margin-bottom: var(--space-lg);
  color: var(--color-primary);
  font-size: var(--text-fine);
  font-weight: 600;
}

.three-step p,
.comparison-grid p,
.concept-card p,
.metric-card p {
  color: var(--color-ink-soft);
}

.example-line {
  padding-top: var(--space-md);
  border-top: 1px solid var(--color-hairline);
}

.rule-card,
.callout {
  margin-top: var(--space-xl);
  padding: var(--space-lg);
  border-radius: var(--radius-lg);
  background: var(--color-canvas-parchment);
}

.rule-card strong {
  color: var(--color-primary);
}

.rule-card p {
  margin-bottom: 0;
}

.term-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: var(--space-lg);
  margin: 0;
}

.term-list div {
  min-width: 0;
  padding: clamp(1.25rem, 3vw, 2rem);
  border: 1px solid var(--color-hairline);
  border-radius: var(--radius-lg);
}

.term-list dt {
  font-family: var(--font-display);
  font-size: var(--text-lead);
  font-weight: 600;
}

.term-list dt span {
  display: block;
  margin-top: var(--space-xs);
  color: var(--color-primary);
  font-family: var(--font-body);
  font-size: var(--text-caption);
}

.term-list dd {
  margin: var(--space-lg) 0 0;
  color: var(--color-ink-soft);
}

.term-list dd .resource-link {
  display: flex;
  width: fit-content;
}

.callout {
  border-left: 3px solid var(--color-primary);
}

.safety {
  margin-top: var(--space-xxl);
}

.safety ul {
  margin: var(--space-lg) 0 0;
  padding: 0;
  border-top: 1px solid var(--color-hairline);
  list-style: none;
}

.safety li {
  display: grid;
  grid-template-columns: minmax(12rem, 0.75fr) 1.25fr;
  gap: var(--space-lg);
  padding: var(--space-lg) 0;
  border-bottom: 1px solid var(--color-hairline);
}

.safety li span {
  color: var(--color-ink-soft);
}

.summary {
  margin-top: var(--space-section);
  margin-bottom: var(--space-section);
  padding: clamp(2rem, 6vw, 5rem);
  border-radius: var(--radius-lg);
  background: var(--color-canvas-parchment);
}

.summary ul {
  max-width: 48rem;
  margin: var(--space-xl) 0;
  padding-left: 1.25rem;
}

.summary li + li {
  margin-top: var(--space-sm);
}

footer {
  padding: var(--space-xl) 1rem;
  border-top: 1px solid var(--color-hairline);
  color: var(--color-ink-muted);
  font-size: var(--text-caption);
  text-align: center;
}

@media (max-width: 52rem) {
  .header-nav {
    display: none;
  }

  .course-link {
    margin-left: auto;
    padding-left: 0;
    border-left: 0;
  }

  .map-grid,
  .metric-grid,
  .split-grid,
  .comparison-grid,
  .term-list {
    grid-template-columns: 1fr 1fr;
  }

  .three-step,
  .learn-more {
    grid-template-columns: 1fr;
  }

  .learn-more a {
    white-space: normal;
  }
}

@media (max-width: 36rem) {
  .hero-inner {
    text-align: left;
  }

  .hero h1,
  .hero-copy {
    margin-left: 0;
  }

  .hero-actions {
    justify-content: flex-start;
  }

  .map-grid,
  .metric-grid,
  .split-grid,
  .comparison-grid,
  .term-list,
  .calculation-list {
    grid-template-columns: 1fr;
  }

  .map-grid a {
    min-height: 0;
  }

  .term-list div,
  .safety li {
    grid-template-columns: 1fr;
    gap: var(--space-sm);
  }

  .chapter {
    padding: var(--space-xxl) 0;
  }

  .chapter-header > p:last-child {
    font-size: var(--text-body);
  }
}

@media print {
  .site-header,
  .hero-actions,
  .map,
  footer {
    display: none;
  }

  .hero-inner,
  .chapter,
  .summary {
    padding-block: 1.5rem;
  }

  .chapter {
    break-before: page;
  }

  .learn-more a::after {
    content: " (" attr(href) ")";
  }
}