/* Repo Research — site styles.
   Layout and typography follow a calm "book reader" pattern: sticky header,
   study rail on the left, article in the middle, outline on the right. */

/* ---------- Tokens ---------- */

:root {
  --bg: #fcfcf9;
  --surface: #f2f3ed;
  --surface-2: #e8eae1;
  --ink: #20231e;
  --muted: #62675d;
  --line: #dedfd7;
  --accent: #d8ed7a;
  --accent-ink: #293019;
  --interactive: #5c761d;   /* text-safe green for hovers and markers */
  --rule-accent: #94a949;   /* decorative rules, active borders */
  --link-line: #a9ba6f;
  --header: rgba(252, 252, 249, 0.92);
  --code-bg: #22261f;
  --code-ink: #e7e9e2;
  --code-muted: #9aa392;
  --code-line: #383d32;
  --shadow: 0 10px 30px rgba(32, 35, 30, 0.08);
  --backdrop: rgba(20, 22, 18, 0.38);

  --sans: "Manrope", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans CJK SC", system-ui, sans-serif;
  --serif: "Newsreader", "Songti SC", "Noto Serif CJK SC", "Source Han Serif SC", "STSong", "SimSun", Georgia, serif;
  --mono: ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;

  --reading-size: 1.0625rem;
  --header-h: 72px;
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #18191c;
    --surface: #222429;
    --surface-2: #2b2e34;
    --ink: #eeeef0;
    --muted: #aaadb6;
    --line: #383b43;
    --accent: #aac7ff;
    --accent-ink: #243d66;
    --interactive: #aac7ff;
    --rule-accent: #aac7ff;
    --link-line: #6582b3;
    --header: rgba(24, 25, 28, 0.94);
    --code-bg: #111215;
    --code-ink: #e6e7ea;
    --code-muted: #8b8f99;
    --code-line: #2d3037;
    --shadow: 0 12px 34px rgba(0, 0, 0, 0.4);
    --backdrop: rgba(0, 0, 0, 0.55);
    color-scheme: dark;
  }
}

:root[data-theme="dark"] {
  --bg: #18191c;
  --surface: #222429;
  --surface-2: #2b2e34;
  --ink: #eeeef0;
  --muted: #aaadb6;
  --line: #383b43;
  --accent: #aac7ff;
  --accent-ink: #243d66;
  --interactive: #aac7ff;
  --rule-accent: #aac7ff;
  --link-line: #6582b3;
  --header: rgba(24, 25, 28, 0.94);
  --code-bg: #111215;
  --code-ink: #e6e7ea;
  --code-muted: #8b8f99;
  --code-line: #2d3037;
  --shadow: 0 12px 34px rgba(0, 0, 0, 0.4);
  --backdrop: rgba(0, 0, 0, 0.55);
  color-scheme: dark;
}

/* ---------- Base ---------- */

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + 20px);
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 1rem;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

a {
  color: inherit;
  text-decoration: none;
}

a,
button {
  -webkit-tap-highlight-color: transparent;
  transition: background-color 0.18s, color 0.18s, border-color 0.18s;
}

button {
  font: inherit;
  color: inherit;
  background: none;
  border: 0;
  cursor: pointer;
}

h1,
h2,
h3,
h4,
p {
  margin-top: 0;
}

img,
svg {
  max-width: 100%;
}

.icon {
  flex: none;
}

[hidden] {
  display: none !important;
}

:focus-visible {
  outline: 2px solid var(--interactive);
  outline-offset: 3px;
  border-radius: 2px;
}

::selection {
  background: var(--accent);
  color: var(--accent-ink);
}

.page-width {
  max-width: 1400px;
  margin-inline: auto;
  padding-inline: 64px;
}

.skip-link {
  position: fixed;
  top: 8px;
  left: 8px;
  z-index: 100;
  padding: 12px 16px;
  background: var(--ink);
  color: var(--bg);
  transform: translateY(-160%);
}

.skip-link:focus {
  transform: none;
}

/* ---------- Shared bits ---------- */

.eyebrow {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 24px;
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.13em;
  text-transform: uppercase;
}

:lang(zh) .eyebrow,
:lang(zh) .rail-label {
  letter-spacing: 0.08em;
}

.badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 29px;
  height: 27px;
  padding: 0 6px;
  background: var(--accent);
  color: var(--accent-ink);
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: 0;
  font-variant-numeric: tabular-nums;
}

.status-dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--rule-accent);
}

.dot {
  color: var(--rule-accent);
}

.button {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  min-height: 48px;
  padding: 12px 22px;
  border: 1px solid transparent;
  border-radius: 2px;
  font-size: 0.875rem;
  font-weight: 700;
  white-space: nowrap;
}

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

.button-primary .icon {
  color: var(--accent);
}

[data-theme="dark"] .button-primary .icon {
  color: var(--accent-ink);
}

.button-primary:hover {
  background: var(--muted);
}

.button-secondary {
  border-color: var(--line);
  background: var(--bg);
}

.button-secondary:hover {
  background: var(--surface);
}

.button-small {
  min-height: 38px;
  padding: 8px 14px;
  gap: 8px;
  font-size: 0.8125rem;
}

.text-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 0.875rem;
  font-weight: 700;
}

.text-link:hover {
  color: var(--interactive);
}

.study-pins {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 4px 14px;
  margin: 0 0 18px;
  color: var(--muted);
  font-size: 0.8125rem;
}

.study-pins a {
  display: inline-flex;
  align-items: baseline;
}

.study-pins code,
.study-pins a span {
  font-family: var(--mono);
  font-size: 0.78rem;
}

.study-pins code {
  color: var(--ink);
}

.study-pins a:hover code {
  text-decoration: underline;
  text-underline-offset: 3px;
}

.pins-label {
  font-size: 0.75rem;
}

/* ---------- Header ---------- */

.site-header {
  position: sticky;
  top: 0;
  z-index: 30;
  height: var(--header-h);
  background: var(--header);
  border-bottom: 1px solid var(--line);
  -webkit-backdrop-filter: saturate(1.4) blur(10px);
  backdrop-filter: saturate(1.4) blur(10px);
}

.site-header-inner {
  display: flex;
  align-items: center;
  gap: 2.5rem;
  max-width: 1600px;
  height: 100%;
  margin-inline: auto;
  padding: 0 40px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 1rem;
  font-weight: 800;
  line-height: 1.25;
  letter-spacing: -0.01em;
  white-space: nowrap;
}

.brand-text {
  display: flex;
  flex-direction: column;
}

.brand-secondary {
  color: var(--muted);
  font-size: 0.8rem;
  font-weight: 500;
  letter-spacing: 0;
}

.brand-mark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 42px;
  padding: 0 2px 5px 0;
  background: var(--ink);
  color: var(--bg);
  font-size: 1.55rem;
  font-weight: 700;
  line-height: 1;
  letter-spacing: -2px;
}

.brand-mark > span {
  color: var(--accent);
}

[data-theme="dark"] .brand-mark > span {
  color: var(--accent-ink);
}

.header-nav {
  display: flex;
  align-items: center;
  gap: 28px;
  margin: auto;
  font-size: 0.875rem;
  font-weight: 600;
}

.header-nav a {
  display: inline-flex;
  align-items: center;
  gap: 4px;
}

.header-nav a:hover {
  color: var(--interactive);
}

.header-tools {
  display: flex;
  align-items: center;
  gap: 12px;
}

.icon-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border: 1px solid var(--line);
  border-radius: 50%;
}

.icon-button:hover {
  background: var(--surface);
}

.sun-icon,
[data-theme="dark"] .moon-icon {
  display: none;
}

.moon-icon,
[data-theme="dark"] .sun-icon {
  display: flex;
}

.menu-button {
  display: none;
}

.language-picker {
  position: relative;
}

.language-picker summary {
  display: flex;
  align-items: center;
  gap: 8px;
  height: 40px;
  padding: 0 12px;
  border: 1px solid var(--line);
  border-radius: 4px;
  font-size: 0.8125rem;
  font-weight: 600;
  list-style: none;
  cursor: pointer;
}

.language-picker summary::-webkit-details-marker {
  display: none;
}

.language-picker summary:hover {
  background: var(--surface);
}

.language-picker nav {
  position: absolute;
  top: calc(100% + 8px);
  right: 0;
  z-index: 40;
  display: flex;
  flex-direction: column;
  min-width: 180px;
  padding: 6px;
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 6px;
  box-shadow: var(--shadow);
}

.language-picker nav a {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 9px 10px;
  border-radius: 4px;
  font-size: 0.8125rem;
}

.language-picker nav a:hover {
  background: var(--surface);
}

.language-picker nav a[aria-current] {
  font-weight: 700;
}

/* ---------- Navigation drawer (small screens) ---------- */

.nav-drawer {
  width: min(360px, 88vw);
  max-width: none;
  height: 100dvh;
  max-height: none;
  margin: 0;
  padding: 18px 22px 28px;
  overflow-y: auto;
  background: var(--bg);
  color: var(--ink);
  border: 0;
  border-right: 1px solid var(--line);
}

.nav-drawer::backdrop {
  background: var(--backdrop);
}

.nav-drawer[open] {
  animation: drawer-in 0.22s ease-out;
}

@keyframes drawer-in {
  from {
    opacity: 0;
    transform: translateX(-24px);
  }
}

.drawer-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 22px;
}

.drawer-links {
  display: flex;
  flex-direction: column;
  margin-bottom: 22px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--line);
}

.drawer-links a {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 10px 2px;
  font-size: 0.9375rem;
  font-weight: 700;
}

.drawer-links a:hover {
  color: var(--interactive);
}

.drawer-rail .back-link {
  display: none;
}

/* ---------- Home ---------- */

.home-hero {
  display: grid;
  grid-template-columns: 1.05fr 1fr;
  align-items: center;
  gap: 72px;
  padding-block: 84px 80px;
}

.hero-copy h1 {
  margin-bottom: 34px;
  font-size: clamp(3.2rem, 5.3vw, 5.25rem);
  font-weight: 750;
  line-height: 0.98;
  letter-spacing: -0.055em;
}

.hero-copy h1 em {
  display: block;
  margin-top: 0.08em;
  font-family: var(--serif);
  font-style: italic;
  font-weight: 500;
  letter-spacing: -0.04em;
}

.hero-lede {
  max-width: 30em;
  margin-bottom: 14px;
  font-size: 1.375rem;
  line-height: 1.5;
  letter-spacing: -0.01em;
}

.hero-note {
  max-width: 34em;
  margin-bottom: 34px;
  color: var(--muted);
  font-size: 0.9375rem;
  line-height: 1.65;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 18px 28px;
}

.panel-head {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  padding-bottom: 18px;
  border-bottom: 1px solid var(--line);
  color: var(--muted);
  font-size: 0.8125rem;
  letter-spacing: 0.04em;
}

.anatomy-list {
  margin: 0;
  padding: 0;
  list-style: none;
}

.anatomy-list li {
  display: flex;
  align-items: baseline;
  gap: 18px;
  padding: 13px 4px;
  border-bottom: 1px solid var(--line);
  font-family: var(--serif);
  font-size: 1.25rem;
  line-height: 1.35;
  letter-spacing: -0.01em;
}

.anatomy-n {
  min-width: 20px;
  color: var(--muted);
  font-family: var(--sans);
  font-size: 0.75rem;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
}

.anatomy-stats {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  margin: 26px 0 0;
}

.anatomy-stats > div {
  display: flex;
  flex-direction: column-reverse;
  justify-content: flex-end;
  gap: 4px;
  padding: 2px 18px 0;
  border-left: 1px solid var(--line);
}

.anatomy-stats > div:first-child {
  padding-left: 0;
  border-left: 0;
}

.anatomy-stats dt {
  color: var(--muted);
  font-size: 0.75rem;
  line-height: 1.4;
}

.anatomy-stats dd {
  margin: 0;
  font-size: 2.4rem;
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: -0.04em;
}

.home-section {
  padding-block: 72px 40px;
}

.home-section > .section-head {
  padding-top: 0;
}

.home-section + .home-section,
.home-hero + .home-section {
  border-top: 1px solid var(--line);
}

.section-head {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 32px;
  margin-bottom: 44px;
}

.section-head .eyebrow {
  margin-bottom: 18px;
}

.section-head h2 {
  margin: 0;
  font-size: clamp(2.6rem, 5vw, 4rem);
  font-weight: 500;
  line-height: 1;
  letter-spacing: -0.05em;
}

.section-aside {
  margin: 0;
  color: var(--muted);
  font-size: 0.875rem;
  line-height: 1.65;
  text-align: right;
}

.study-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0 56px;
}

.study-card {
  display: flex;
  flex-direction: column;
  padding: 30px 0 44px;
  border-top: 1px solid var(--line);
}

.study-card-head {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 18px;
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.study-card h3 {
  margin-bottom: 12px;
  font-size: 2.25rem;
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: -0.045em;
}

.study-card h3 a:hover {
  color: var(--interactive);
}

.study-card-tagline {
  margin-bottom: 12px;
  font-family: var(--serif);
  font-size: 1.125rem;
  line-height: 1.6;
}

.study-card-tagline p {
  margin: 0;
}

.study-card-tagline--zh {
  color: var(--muted);
  font-size: 1rem;
  line-height: 1.85;
}

.study-card-tagline code,
.method-list code,
.diagram-question code,
.diagram-card-foot code {
  padding: 0.08em 0.3em;
  background: var(--surface);
  border-radius: 3px;
  font-family: var(--mono);
  font-size: 0.8em;
}

.study-card-status {
  display: flex;
  align-items: flex-start;
  gap: 8px;
  margin: 6px 0 26px;
  color: var(--muted);
  font-size: 0.8125rem;
  line-height: 1.55;
}

.study-card-status .icon {
  margin-top: 2px;
  color: var(--interactive);
}

.study-card-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 12px 20px;
  margin-top: auto;
}

.diagram-group {
  padding: 26px 0 32px;
  border-top: 1px solid var(--line);
}

.diagram-group-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 18px;
}

.diagram-group-head h3 {
  display: flex;
  align-items: center;
  gap: 12px;
  margin: 0;
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: -0.03em;
}

.chip-list {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.chip {
  display: inline-flex;
  align-items: baseline;
  gap: 8px;
  padding: 9px 15px;
  border: 1px solid var(--line);
  border-radius: 999px;
  font-size: 0.875rem;
  font-weight: 600;
}

.chip small {
  color: var(--muted);
  font-size: 0.72rem;
  font-weight: 500;
}

.chip:hover {
  background: var(--surface);
  border-color: var(--rule-accent);
}

.method-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0 56px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.method-list li {
  display: grid;
  grid-template-columns: 44px 1fr;
  align-content: start;
  column-gap: 8px;
  padding: 24px 0 28px;
  border-top: 1px solid var(--line);
}

.method-n {
  grid-row: span 2;
  padding-top: 5px;
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
}

.method-list h3 {
  margin: 0 0 8px;
  font-size: 1.125rem;
  font-weight: 700;
  letter-spacing: -0.025em;
}

.method-list p {
  margin: 0;
  color: var(--muted);
  font-size: 0.9375rem;
  line-height: 1.65;
}

.home-notes {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(0, 1.5fr);
  align-items: start;
  gap: 48px;
  padding-bottom: 80px;
}

.home-notes .section-head {
  margin: 0;
}

.site-footer {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  padding-block: 36px 48px;
  border-top: 1px solid var(--line);
}

.site-footer nav {
  display: flex;
  flex-wrap: wrap;
  gap: 24px;
  font-size: 0.875rem;
  font-weight: 600;
}

.site-footer nav a {
  display: inline-flex;
  align-items: center;
  gap: 4px;
}

.site-footer nav a:hover {
  color: var(--interactive);
}

/* ---------- Reader layout ---------- */

.reading-progress {
  position: fixed;
  top: var(--header-h);
  right: 0;
  left: 0;
  z-index: 31;
  height: 2px;
  pointer-events: none;
}

.reading-progress > div {
  height: 100%;
  background: var(--rule-accent);
  transform: scaleX(0);
  transform-origin: 0 50%;
}

.reader-grid {
  display: grid;
  grid-template-columns: 250px minmax(0, 1fr) 240px;
  align-items: start;
  max-width: 1600px;
  margin: 0 auto;
}

.reader-grid--wide {
  grid-template-columns: 250px minmax(0, 1fr);
}

.study-rail,
.outline-rail {
  position: sticky;
  top: var(--header-h);
  overflow-y: auto;
  overscroll-behavior: contain;
  scrollbar-width: thin;
}

.study-rail {
  height: calc(100vh - var(--header-h));
  height: calc(100dvh - var(--header-h));
  padding: 32px 18px 28px 24px;
  border-right: 1px solid var(--line);
}

.back-link {
  display: flex;
  align-items: center;
  gap: 9px;
  margin-bottom: 34px;
  color: var(--muted);
  font-size: 0.8125rem;
}

.back-link:hover {
  color: var(--ink);
}

.rail-label {
  margin-bottom: 16px;
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 750;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.rail-nav {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.rail-study {
  display: flex;
  align-items: flex-start;
  gap: 11px;
  padding: 10px 9px;
  border-radius: 3px;
  color: var(--muted);
  font-size: 0.875rem;
  line-height: 1.5;
}

.rail-study:hover {
  background: var(--surface);
  color: var(--ink);
}

.rail-study.is-current {
  padding-left: 7px;
  background: var(--surface);
  border-left: 2px solid var(--rule-accent);
  color: var(--ink);
  font-weight: 700;
}

.rail-number {
  flex: none;
  padding-top: 2px;
  font-size: 0.75rem;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  opacity: 0.7;
}

.rail-sub {
  display: flex;
  flex-direction: column;
  gap: 2px;
  margin: 6px 0 10px 17px;
  padding-left: 10px;
  border-left: 1px solid var(--line);
}

.rail-sub a {
  display: flex;
  align-items: center;
  gap: 9px;
  padding: 7px 8px;
  border-radius: 3px;
  color: var(--muted);
  font-size: 0.8125rem;
  line-height: 1.4;
}

.rail-sub a:hover {
  background: var(--surface);
  color: var(--ink);
}

.rail-sub a[aria-current] {
  color: var(--ink);
  font-weight: 700;
}

.rail-sub a > :last-child:not(span) {
  margin-left: auto;
}

.rail-sub small {
  margin-left: auto;
  color: var(--muted);
  font-size: 0.72rem;
  font-variant-numeric: tabular-nums;
}

.rail-bottom {
  display: flex;
  flex-direction: column;
  gap: 16px;
  margin-top: 30px;
  padding-top: 22px;
  border-top: 1px solid var(--line);
}

.rail-bottom a {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--muted);
  font-size: 0.8125rem;
}

.rail-bottom a:hover {
  color: var(--ink);
}

.reading-main {
  width: 100%;
  min-width: 0;
  max-width: 880px;
  margin: 0 auto;
  padding: 36px 56px 0;
}

.reading-main--wide {
  max-width: 1120px;
}

.reader-topline {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 6px 10px;
  margin-bottom: 46px;
  color: var(--muted);
  font-size: 0.8125rem;
}

.reader-topline a:hover {
  color: var(--ink);
  text-decoration: underline;
  text-underline-offset: 3px;
}

.reading-time {
  margin-left: auto;
  white-space: nowrap;
}

.study-heading .eyebrow {
  gap: 12px;
  margin-bottom: 22px;
}

.study-heading h1 {
  margin-bottom: 26px;
  font-size: clamp(2.6rem, 4.2vw, 3.9rem);
  font-weight: 700;
  line-height: 1.05;
  letter-spacing: -0.055em;
}

.study-toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 12px 20px;
  margin-bottom: 34px;
  padding-bottom: 18px;
  border-bottom: 1px solid var(--line);
}

.study-toolbar .study-pins {
  margin: 0;
}

.study-links {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 18px;
  margin: 0;
  font-size: 0.8125rem;
  font-weight: 700;
}

.study-links a {
  display: inline-flex;
  align-items: center;
  gap: 7px;
}

.study-links a:hover {
  color: var(--interactive);
}

.reader-controls {
  display: flex;
  align-items: center;
  gap: 4px;
  color: var(--muted);
  font-size: 0.8125rem;
}

.text-size {
  position: relative;
}

.text-size summary,
.focus-toggle {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 6px 8px;
  border-radius: 3px;
  white-space: nowrap;
  cursor: pointer;
}

.text-size summary {
  list-style: none;
}

.text-size summary::-webkit-details-marker {
  display: none;
}

.text-size summary:hover,
.focus-toggle:hover {
  background: var(--surface);
  color: var(--ink);
}

.type-icon {
  color: var(--ink);
  font-family: var(--serif);
  font-size: 1.15rem;
  line-height: 1;
}

.text-size-panel {
  position: absolute;
  top: calc(100% + 8px);
  right: 0;
  z-index: 20;
  min-width: 220px;
  padding: 18px;
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 6px;
  box-shadow: var(--shadow);
  color: var(--ink);
  font-size: 0.8125rem;
}

.text-size-panel > div {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-top: 12px;
}

.text-size-panel > div button {
  width: 42px;
  height: 38px;
  border: 1px solid var(--line);
  border-radius: 3px;
}

.text-size-panel > div button:hover {
  background: var(--surface);
}

.text-size-panel output {
  min-width: 44px;
  text-align: center;
  font-variant-numeric: tabular-nums;
}

.text-size-reset {
  margin-top: 12px;
  padding: 4px 0;
  font-size: 0.75rem;
  text-decoration: underline;
  text-underline-offset: 3px;
}

.focus-toggle[aria-pressed="true"] {
  background: var(--accent);
  color: var(--accent-ink);
}

.mobile-outline {
  display: none;
  margin-bottom: 30px;
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 4px;
}

.mobile-outline summary {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 13px 16px;
  font-size: 0.8125rem;
  font-weight: 700;
  list-style: none;
  cursor: pointer;
}

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

.mobile-outline summary span::before {
  content: "+";
  font-size: 1.2rem;
  font-weight: 400;
}

.mobile-outline[open] summary span::before {
  content: "−";
}

.mobile-outline nav {
  display: flex;
  flex-direction: column;
  max-height: 60vh;
  padding: 0 16px 14px;
  overflow-y: auto;
}

.mobile-outline a {
  padding: 7px 0;
  color: var(--muted);
  font-size: 0.875rem;
  line-height: 1.45;
}

.mobile-outline a.is-sub {
  padding-left: 14px;
  font-size: 0.8125rem;
}

.mobile-outline a:hover,
.mobile-outline a[aria-current="location"] {
  color: var(--ink);
}

.outline-rail {
  max-height: calc(100vh - var(--header-h));
  max-height: calc(100dvh - var(--header-h));
  padding: 44px 24px 30px 8px;
}

.outline {
  display: flex;
  flex-direction: column;
  border-left: 1px solid var(--line);
}

.outline a {
  margin-left: -1px;
  padding: 6px 0 6px 15px;
  border-left: 2px solid transparent;
  color: var(--muted);
  font-size: 0.8125rem;
  line-height: 1.45;
}

.outline a.is-sub {
  padding-left: 26px;
  font-size: 0.78rem;
}

.outline a:hover {
  color: var(--ink);
}

.outline a[aria-current="location"] {
  border-left-color: var(--rule-accent);
  color: var(--ink);
  font-weight: 650;
}

.back-to-top {
  display: flex;
  align-items: center;
  gap: 10px;
  margin: 22px 0 0 15px;
  color: var(--muted);
  font-size: 0.8125rem;
}

.back-to-top:hover {
  color: var(--ink);
}

.study-end {
  margin: 64px 0 36px;
  padding: 34px;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 4px;
}

.study-end .eyebrow {
  margin-bottom: 12px;
}

.study-end h2 {
  margin-bottom: 12px;
  font: 500 2.5rem/1.1 var(--serif);
  letter-spacing: -0.03em;
}

.study-end p {
  max-width: 40em;
  margin-bottom: 24px;
  color: var(--muted);
  font-size: 0.9375rem;
  line-height: 1.7;
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.pager {
  display: flex;
  justify-content: space-between;
  gap: 24px;
  padding-block: 24px;
  border-block: 1px solid var(--line);
}

.pager a {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.pager span {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  color: var(--muted);
  font-size: 0.75rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.pager strong {
  font-size: 0.9375rem;
  font-weight: 700;
}

.pager a:hover strong {
  text-decoration: underline;
  text-underline-offset: 4px;
}

.pager-next {
  align-items: flex-end;
  margin-left: auto;
  text-align: right;
}

.reader-footer {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 12px 24px;
  padding-block: 26px 44px;
  color: var(--muted);
  font-size: 0.8125rem;
}

.reader-footer a {
  display: inline-flex;
  align-items: center;
  gap: 5px;
}

.reader-footer a:hover {
  color: var(--ink);
}

/* ---------- Diagram gallery ---------- */

.diagram-cards {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
  margin: 8px 0 52px;
  padding: 0;
  list-style: none;
}

.diagram-card {
  display: flex;
  flex-direction: column;
  height: 100%;
  padding: 20px 20px 18px;
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 6px;
}

.diagram-card:hover {
  background: var(--surface);
  border-color: var(--rule-accent);
}

.diagram-card-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 18px;
}

.diagram-number {
  color: var(--muted);
  font-size: 0.75rem;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
}

.diagram-type {
  padding: 3px 9px;
  background: var(--surface);
  border-radius: 999px;
  color: var(--muted);
  font-size: 0.6875rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}

.diagram-card:hover .diagram-type {
  background: var(--accent);
  color: var(--accent-ink);
}

.diagram-title {
  margin-bottom: 8px;
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: -0.03em;
}

.diagram-question {
  font-family: var(--serif);
  font-size: 1rem;
  line-height: 1.55;
}

.diagram-question--zh {
  margin-top: 6px;
  color: var(--muted);
  font-size: 0.9375rem;
  line-height: 1.7;
}

.diagram-card-foot {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-top: auto;
  padding-top: 20px;
  color: var(--muted);
  font-size: 0.75rem;
}

.diagram-card-foot .icon {
  transition: transform 0.18s;
}

.diagram-card:hover .diagram-card-foot .icon {
  color: var(--interactive);
  transform: translateX(3px);
}

/* ---------- Prose ---------- */

.prose {
  font-family: var(--serif);
  font-size: calc(var(--reading-size) * var(--reading-scale, 1));
  line-height: 1.7;
  overflow-wrap: break-word;
}

:lang(zh) .prose {
  line-height: 1.9;
}

.prose > :first-child {
  margin-top: 0;
}

.prose p {
  margin: 0 0 1.25em;
}

.prose h2,
.prose h3,
.prose h4 {
  position: relative;
  font-family: var(--sans);
  line-height: 1.3;
  letter-spacing: -0.03em;
  text-wrap: balance;
}

.prose h2 {
  margin: 2.4em 0 0.9em;
  padding-top: 26px;
  border-top: 1px solid var(--line);
  font-size: 1.65em;
  font-weight: 700;
}

.prose h3 {
  margin: 2em 0 0.8em;
  font-size: 1.2em;
  font-weight: 700;
}

.prose h4 {
  margin: 1.7em 0 0.7em;
  font-size: 1.02em;
  font-weight: 700;
}

.prose hr {
  margin: 2.6em 0;
  border: 0;
  border-top: 1px solid var(--line);
}

.prose hr + h2 {
  margin-top: 0;
  padding-top: 0;
  border-top: 0;
}

.heading-anchor {
  position: absolute;
  left: -1.05em;
  padding-right: 0.3em;
  color: var(--muted);
  font-weight: 400;
  opacity: 0;
}

.prose h2 .heading-anchor {
  top: 26px;
}

.prose hr + h2 .heading-anchor {
  top: 0;
}

.prose h2:hover .heading-anchor,
.prose h3:hover .heading-anchor,
.heading-anchor:focus-visible {
  opacity: 1;
}

.prose a {
  text-decoration: underline;
  text-decoration-color: var(--link-line);
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
}

.prose a:hover {
  color: var(--interactive);
  text-decoration-color: currentColor;
}

.prose a.heading-anchor {
  text-decoration: none;
}

.prose strong {
  font-weight: 650;
}

.prose ul,
.prose ol {
  margin: 1em 0 1.6em;
  padding-left: 1.4em;
}

.prose li {
  margin: 0.45em 0;
  padding-left: 0.15em;
}

.prose li::marker {
  color: var(--interactive);
}

.prose li > p {
  margin-bottom: 0.6em;
}

.prose li > ul,
.prose li > ol {
  margin: 0.4em 0 0.6em;
}

.prose blockquote {
  margin: 1.8em 0;
  padding: 20px 24px 2px;
  background: var(--surface);
  border-left: 2px solid var(--rule-accent);
  border-radius: 0 4px 4px 0;
  font-size: 0.95em;
}

.prose blockquote p {
  margin-bottom: 1em;
}

.prose code {
  padding: 0.1em 0.32em;
  background: var(--surface);
  border-radius: 3px;
  font-family: var(--mono);
  font-size: 0.8em;
  overflow-wrap: anywhere;
}

.prose blockquote code {
  background: var(--surface-2);
}

.prose pre {
  margin: 1.5em 0 2em;
  padding: 20px 22px;
  overflow-x: auto;
  background: var(--code-bg);
  border-radius: 6px;
  color: var(--code-ink);
  font-size: 0.8em;
  line-height: 1.7;
  tab-size: 2;
}

.prose pre code {
  padding: 0;
  background: none;
  border-radius: 0;
  color: inherit;
  font-size: inherit;
  overflow-wrap: normal;
  white-space: pre;
}

.prose div.highlighter-rouge {
  margin: 1.5em 0 2em;
  overflow: hidden;
  background: var(--code-bg);
  border-radius: 6px;
}

.prose div.highlighter-rouge pre,
.prose div.highlight {
  margin: 0;
  border-radius: 0;
}

[data-theme="dark"] .prose pre,
[data-theme="dark"] .prose div.highlighter-rouge {
  border: 1px solid var(--code-line);
}

[data-theme="dark"] .prose div.highlighter-rouge pre {
  border: 0;
}

.code-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 7px 10px 7px 22px;
  border-bottom: 1px solid var(--code-line);
  color: var(--code-muted);
  font-family: var(--sans);
  font-size: 0.7rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.copy-code {
  padding: 3px 10px;
  border: 1px solid var(--code-line);
  border-radius: 3px;
  color: var(--code-ink);
  font: 600 0.72rem var(--sans);
  letter-spacing: 0.02em;
  text-transform: none;
}

.copy-code:hover {
  background: rgba(255, 255, 255, 0.08);
}

.prose table {
  display: block;
  width: 100%;
  max-width: 100%;
  margin: 1.8em 0 2.2em;
  overflow-x: auto;
  border: 1px solid var(--line);
  border-collapse: collapse;
  border-radius: 4px;
  font-family: var(--sans);
  font-size: 0.8em;
  line-height: 1.6;
}

.prose th,
.prose td {
  min-width: 110px;
  padding: 11px 14px;
  border-bottom: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

.prose th:not(:last-child),
.prose td:not(:last-child) {
  border-right: 1px solid var(--line);
}

.prose th {
  background: var(--surface);
  font-weight: 700;
}

.prose tbody tr:last-child td {
  border-bottom: 0;
}

.mermaid-figure {
  position: relative;
  margin: 1.5em 0 2em;
}

.prose .mermaid-figure pre.mermaid {
  margin: 0;
  padding: 28px 16px 20px;
  background: var(--surface);
  border: 1px solid var(--line);
  color: var(--ink);
  font-family: var(--sans);
  text-align: center;
}

.prose pre.mermaid:not([data-processed]):not(.is-failed) {
  min-height: 140px;
  color: transparent;
}

/* Diagrams render at their natural size; wide ones scroll or open in a dialog. */
.prose pre.mermaid svg,
.figure-dialog svg {
  display: block;
  max-width: none;
  height: auto;
  margin: 0 auto;
}

.figure-expand {
  position: absolute;
  top: 8px;
  right: 8px;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 9px;
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 3px;
  color: var(--muted);
  font: 600 0.72rem var(--sans);
}

.figure-expand:hover {
  color: var(--ink);
  background: var(--surface);
}

.figure-dialog {
  width: 96vw;
  max-width: none;
  height: 92vh;
  max-height: none;
  padding: 0;
  overflow: hidden;
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
  color: var(--ink);
}

.figure-dialog::backdrop {
  background: var(--backdrop);
}

.figure-dialog-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  height: 56px;
  padding: 0 10px 0 20px;
  border-bottom: 1px solid var(--line);
  color: var(--muted);
  font-size: 0.8125rem;
}

.figure-dialog-body {
  height: calc(100% - 56px);
  padding: 28px;
  overflow: auto;
  background: var(--surface);
}

.prose--gallery {
  max-width: 760px;
}

.prose--notes {
  color: var(--muted);
  font-size: calc(var(--reading-size) * 0.92);
}

.prose--compact {
  font-size: 1.0625rem;
}

.prose--compact ul {
  margin-top: 0.4em;
}

/* Rouge tokens (code blocks are dark in both themes) */
.highlight .c, .highlight .c1, .highlight .cm, .highlight .cs, .highlight .cp, .highlight .ch, .highlight .cpf { color: #8b949e; font-style: italic; }
.highlight .k, .highlight .kd, .highlight .kn, .highlight .kp, .highlight .kr, .highlight .kt, .highlight .kc, .highlight .ow { color: #ff7b72; }
.highlight .s, .highlight .s1, .highlight .s2, .highlight .sb, .highlight .sc, .highlight .sd, .highlight .se, .highlight .sh, .highlight .si, .highlight .sx, .highlight .sr, .highlight .ss, .highlight .dl, .highlight .sa { color: #a5d6ff; }
.highlight .nf, .highlight .fm, .highlight .nd { color: #d2a8ff; }
.highlight .nc, .highlight .nn, .highlight .nb, .highlight .bp, .highlight .ne { color: #ffa657; }
.highlight .m, .highlight .mi, .highlight .mf, .highlight .mh, .highlight .mo, .highlight .mb, .highlight .il { color: #79c0ff; }
.highlight .na, .highlight .nv, .highlight .vi, .highlight .vc, .highlight .vg, .highlight .no { color: #79c0ff; }
.highlight .nt { color: #7ee787; }
.highlight .gi { color: #aff5b4; background: rgba(46, 160, 67, 0.15); }
.highlight .gd { color: #ffdcd7; background: rgba(248, 81, 73, 0.15); }
.highlight .gh, .highlight .gu { color: #79c0ff; font-weight: 700; }
.highlight .err { color: inherit; background: none; }

/* ---------- Focus mode ---------- */

.focus-reading .study-rail,
.focus-reading .outline-rail {
  display: none;
}

.focus-reading .reader-grid {
  display: block;
}

.focus-reading .reading-main {
  max-width: 860px;
}

.focus-reading .mobile-outline {
  display: block;
}

/* ---------- Responsive ---------- */

@media (max-width: 1240px) {
  .reader-grid {
    grid-template-columns: 230px minmax(0, 1fr);
  }

  .outline-rail {
    display: none;
  }

  .mobile-outline {
    display: block;
  }
}

@media (max-width: 1080px) {
  .page-width {
    padding-inline: 40px;
  }

  .home-hero {
    grid-template-columns: 1fr;
    gap: 52px;
    padding-block: 60px 64px;
  }

  .study-list,
  .method-list {
    grid-template-columns: 1fr;
  }

  .home-notes {
    grid-template-columns: 1fr;
    gap: 24px;
  }
}

@media (max-width: 900px) {
  .header-nav {
    display: none;
  }

  .header-tools {
    margin-left: auto;
  }

  .menu-button {
    display: inline-flex;
  }

  .reader-grid,
  .reader-grid--wide {
    display: block;
  }

  .study-rail {
    display: none;
  }

  .reading-main {
    max-width: 760px;
    padding: 26px 24px 0;
  }

  .reading-main--wide {
    max-width: none;
  }

  .focus-toggle {
    display: none;
  }
}

@media (max-width: 640px) {
  :root {
    --header-h: 64px;
  }

  .site-header-inner {
    gap: 12px;
    padding: 0 16px;
  }

  .header-tools {
    gap: 8px;
  }

  .language-picker .current-language {
    display: none;
  }

  .page-width {
    padding-inline: 20px;
  }

  .home-hero {
    padding-block: 44px 52px;
  }

  .hero-copy h1 {
    margin-bottom: 26px;
    font-size: clamp(2.8rem, 13vw, 4rem);
  }

  .hero-lede {
    font-size: 1.15rem;
  }

  .anatomy-list li {
    font-size: 1.1rem;
  }

  .anatomy-stats dd {
    font-size: 2rem;
  }

  .home-section {
    padding-block: 52px 28px;
  }

  .section-head {
    flex-direction: column;
    align-items: flex-start;
    gap: 14px;
    margin-bottom: 30px;
  }

  .section-aside {
    text-align: left;
  }

  .study-card h3 {
    font-size: 1.9rem;
  }

  .reading-main {
    padding: 22px 18px 0;
  }

  .reader-topline {
    margin-bottom: 30px;
  }

  .study-heading h1 {
    font-size: 2.5rem;
  }

  .control-label {
    display: none;
  }

  .prose {
    font-size: calc(var(--reading-size) * var(--reading-scale, 1) * 0.95);
  }

  .prose > pre,
  .prose > div.highlighter-rouge,
  .prose > .mermaid-figure {
    margin-inline: -18px;
    border-radius: 0;
  }

  .figure-dialog {
    width: 100vw;
    height: 100dvh;
    border-radius: 0;
  }

  .prose blockquote {
    padding: 16px 18px 2px;
  }

  .prose th,
  .prose td {
    padding: 9px 11px;
  }

  .study-end {
    padding: 24px;
  }

  .study-end h2 {
    font-size: 2rem;
  }

  .diagram-cards {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 420px) {
  .site-header .brand-text {
    display: none;
  }
}

@media (hover: none) {
  .heading-anchor {
    display: none;
  }
}

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

  *,
  *::before,
  *::after {
    transition: none !important;
    animation: none !important;
  }
}

@media print {
  .site-header,
  .study-rail,
  .outline-rail,
  .reading-progress,
  .mobile-outline,
  .reader-controls,
  .study-end,
  .pager,
  .code-toolbar {
    display: none !important;
  }

  .reader-grid {
    display: block;
  }
}