:root {
  --color-surface: #f0eeef;
  --color-surface-alt: #e8e5e6;
  --color-surface-deep: #ddd9da;
  --color-ink: #503f40;
  --color-ink-soft: #7a6264;
  --color-ink-muted: #8c7375;
  --color-line: #d3ced0;
  --color-primary: #d52a39;
  --color-primary-ink: #ffffff;
  --color-primary-soft: #ecd3d6;
  --color-accent: #b2621a;
  --color-accent-ink: #ffffff;
  --color-highlight: #e5d5c9;
  --color-focus: #a4550e;
  --color-contrast-surface: #1b0f10;
  --color-contrast-ink: #e7e4e4;
  --color-contrast-line: #483e3f;
  --color-contrast-accent: #de7a21;
  --overlay-scrim: linear-gradient(180deg, rgba(27, 15, 16, 0.35) 0%, rgba(27, 15, 16, 0.72) 55%, rgba(27, 15, 16, 0.92) 100%);
  --font-heading: "Songti SC", STSong, "Source Han Serif SC", SimSun, serif;
  --font-body: "Songti SC", STSong, "Source Han Serif SC", SimSun, serif;
  --font-mono: ui-monospace, Menlo, Consolas, monospace;
  --text-xs: 12.2px;
  --text-sm: 14.6px;
  --text-base: 16px;
  --text-lg: 19.2px;
  --text-xl: 23.0px;
  --text-2xl: 27.6px;
  --text-3xl: 33.2px;
  --text-4xl: 39.8px;
  --text-display: clamp(36px, 7.4vw, 95px);
  --text-figure: clamp(30px, 5.3vw, 68px);
  --weight-heading: 603;
  --weight-body: 400;
  --leading-body: 1.8;
  --leading-heading: 1.22;
  --tracking-heading: 0.03em;
  --radius-sm: 1px;
  --radius-md: 1px;
  --radius-lg: 1px;
  --radius-pill: 1px;
  --border-thin: 1px;
  --border-thick: 2px;
  --shadow-1: none;
  --shadow-2: none;
  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 32px;
  --space-6: 48px;
  --space-8: 64px;
  --container: 1060px;
  --measure: 73ch;
  --gutter: 32px;
  --section-y: 91px;
  --section-y-lg: 127px;
}

/* ============================================================
   2. 重置与基础
   ============================================================ */
*, *::before, *::after { box-sizing: border-box; }

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

body {
  margin: 0;
  padding-top: calc(var(--space-8) + var(--space-3));
  background-color: var(--color-surface);
  color: var(--color-ink);
  font-family: var(--font-body);
  font-size: var(--text-base);
  font-weight: var(--weight-body);
  line-height: var(--leading-body);
  letter-spacing: 0.01em;
  overflow-wrap: break-word;
  -webkit-font-smoothing: antialiased;
}

html.has-hero-dark body { padding-top: 0; }

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

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

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

ul, ol { margin: 0; padding: 0; list-style: none; }

h1, h2, h3, h4, h5, h6, p, figure, blockquote, dl, dd { margin: 0; }

table { border-collapse: collapse; border-spacing: 0; }

:focus-visible {
  outline: var(--border-thick) solid var(--color-focus);
  outline-offset: 2px;
}

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

/* ---------- 3. 中文排版 ---------- */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  line-height: var(--leading-heading);
  letter-spacing: var(--tracking-heading);
  color: var(--color-ink);
}

h1 { font-size: var(--text-4xl); }
h2 { font-size: var(--text-3xl); }
h3 { font-size: var(--text-xl); }
h4 { font-size: var(--text-lg); }

.prose p, .lede {
  text-align: justify;
  text-justify: inter-ideograph;
}

.prose { max-width: var(--measure); }
.prose p + p { margin-top: var(--space-3); }
.prose h2 { font-size: var(--text-2xl); margin-block: var(--space-6) var(--space-3); }
.prose h3 { font-size: var(--text-xl); margin-block: var(--space-4) var(--space-2); }
.prose ul, .prose ol { margin-block: var(--space-2); padding-left: 1.4em; list-style: disc; }
.prose ol { list-style: decimal; }
.prose li + li { margin-top: var(--space-1); }
.prose a { color: var(--color-primary); border-bottom: var(--border-thin) solid var(--color-primary-soft); }

.lede {
  font-size: var(--text-lg);
  line-height: 1.7;
  color: var(--color-ink-soft);
  max-width: var(--measure);
}

.mono, .num {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  letter-spacing: 0.02em;
}

/* ---------- 4. 容器 · 分节 · 网格 ---------- */
.shell {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: var(--space-4);
}

.section { padding-block: var(--section-y); }
.section--lg { padding-block: var(--section-y-lg); }

.section--deep {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}
.section--deep h1, .section--deep h2, .section--deep h3, .section--deep h4 { color: var(--color-contrast-ink); }
.section--deep .lede, .section--deep .section-head__note { color: color-mix(in srgb, var(--color-contrast-ink) 76%, transparent); }

.grid { display: grid; gap: var(--gutter); }
.grid--2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.grid--3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
.grid--4 { grid-template-columns: repeat(4, minmax(0, 1fr)); }

/* ---------- 5. 通用组件 ---------- */
.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.22em;
  color: var(--color-accent);
}
.eyebrow::before {
  content: "";
  width: 14px;
  height: var(--border-thick);
  background-color: var(--color-primary);
}
.section--deep .eyebrow { color: var(--color-contrast-accent); }
.section--deep .eyebrow::before { background-color: var(--color-contrast-accent); }

.section-head {
  text-align: center;
  margin-bottom: var(--space-6);
}
.section-head__title {
  margin-top: var(--space-2);
  font-size: var(--text-3xl);
}
.section-head__note {
  margin-top: var(--space-2);
  margin-inline: auto;
  max-width: 48ch;
  font-size: var(--text-sm);
  color: var(--color-ink-soft);
}

.figure-text {
  font-family: var(--font-mono);
  font-size: var(--text-figure);
  font-weight: var(--weight-heading);
  line-height: 1;
  letter-spacing: -0.02em;
  font-variant-numeric: tabular-nums;
  color: var(--color-primary);
}
.section--deep .figure-text { color: var(--color-contrast-accent); }

.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-2) var(--space-4);
  border: var(--border-thin) solid var(--color-ink);
  border-radius: var(--radius-sm);
  background-color: transparent;
  color: var(--color-ink);
  font-size: var(--text-sm);
  letter-spacing: 0.14em;
  line-height: 1.4;
  transition: background-color 0.18s ease, color 0.18s ease, border-color 0.18s ease;
}
.btn:hover {
  background-color: var(--color-contrast-surface);
  border-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}
.btn--primary {
  background-color: var(--color-primary);
  border-color: var(--color-primary);
  color: var(--color-primary-ink);
}
.btn--primary:hover {
  background-color: var(--color-contrast-surface);
  border-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}
.btn--onDark {
  border-color: var(--color-contrast-line);
  color: var(--color-contrast-ink);
}
.btn--onDark:hover {
  background-color: var(--color-contrast-ink);
  border-color: var(--color-contrast-ink);
  color: var(--color-contrast-surface);
}

.tag {
  display: inline-block;
  padding: 2px var(--space-1);
  border-radius: var(--radius-sm);
  background-color: var(--color-primary-soft);
  color: var(--color-primary);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  line-height: 1.6;
}
.tag--accent {
  background-color: color-mix(in srgb, var(--color-accent) 16%, var(--color-surface));
  color: var(--color-accent);
}
.section--deep .tag {
  background-color: color-mix(in srgb, var(--color-contrast-accent) 22%, transparent);
  color: var(--color-contrast-accent);
}

.panel {
  background-color: var(--color-surface-alt);
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
  padding: var(--space-4);
}
.panel--deep { background-color: var(--color-surface-deep); }
.panel--dark {
  background-color: var(--color-contrast-surface);
  border-color: var(--color-contrast-line);
  color: var(--color-contrast-ink);
}
.panel--dark h3, .panel--dark h4 { color: var(--color-contrast-ink); }

.data-table {
  width: 100%;
  font-size: var(--text-sm);
  background-color: transparent;
}
.data-table caption {
  padding-bottom: var(--space-2);
  text-align: left;
  font-size: var(--text-xs);
  letter-spacing: 0.2em;
  color: var(--color-accent);
}
.data-table th, .data-table td {
  padding: var(--space-2) var(--space-3);
  border-bottom: var(--border-thin) solid var(--color-line);
  text-align: left;
  vertical-align: top;
}
.data-table thead th {
  border-bottom: var(--border-thick) solid var(--color-primary);
  font-weight: var(--weight-heading);
  letter-spacing: 0.08em;
}
.data-table tbody tr:nth-child(even) { background-color: var(--color-surface-alt); }
.data-table tbody tr:hover { background-color: var(--color-highlight); }
.data-table .num { text-align: right; }

.media-frame {
  position: relative;
  display: block;
  overflow: hidden;
  aspect-ratio: 16 / 10;
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
  background-color: var(--color-surface-deep);
}
.media-frame > img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}
.media-frame--wide { aspect-ratio: 21 / 9; }
.media-frame--portrait { aspect-ratio: 3 / 4; }
.media-frame--dark {
  background-color: var(--color-contrast-surface);
  border-color: var(--color-contrast-line);
}
.media-frame__scrim::after {
  content: "";
  position: absolute;
  inset: 0;
  background: var(--overlay-scrim);
  pointer-events: none;
}
.media-frame__label {
  position: absolute;
  left: 0;
  bottom: 0;
  z-index: 2;
  padding: var(--space-2) var(--space-3);
  color: var(--color-contrast-ink);
  font-size: var(--text-sm);
  letter-spacing: 0.08em;
}

.breadcrumb {
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: var(--color-ink-muted);
}
.breadcrumb ol {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-1);
}
.breadcrumb li::after {
  content: "／";
  margin-left: var(--space-1);
  color: var(--color-line);
}
.breadcrumb li:last-child::after { content: none; }
.breadcrumb a:hover { color: var(--color-primary); }

.rule-mark {
  height: 5px;
  border: 0;
  border-top: var(--border-thick) solid var(--color-primary);
  border-bottom: var(--border-thin) solid var(--color-line);
  margin-block: var(--space-4);
}
.rule-double {
  height: 0;
  border: 0;
  border-top: 3px double var(--color-ink-soft);
  margin-block: var(--space-6);
}
.fret-band {
  height: 10px;
  border-top: var(--border-thin) solid var(--color-line);
  border-bottom: var(--border-thick) solid var(--color-primary);
  background-image: repeating-linear-gradient(90deg, var(--color-line) 0 1px, transparent 1px 10px);
  margin-block: var(--space-4);
}
.section--deep .fret-band {
  border-top-color: var(--color-contrast-line);
  border-bottom-color: var(--color-contrast-accent);
  background-image: repeating-linear-gradient(90deg, var(--color-contrast-line) 0 1px, transparent 1px 10px);
}

.toc-rail {
  position: sticky;
  top: calc(var(--space-8) + var(--space-4));
  font-size: var(--text-sm);
}
.toc-rail__title {
  font-size: var(--text-xs);
  letter-spacing: 0.2em;
  color: var(--color-accent);
  margin-bottom: var(--space-2);
}
.toc-rail ol { display: grid; gap: var(--space-1); }
.toc-rail a {
  display: block;
  padding: var(--space-1) var(--space-1) var(--space-1) var(--space-2);
  border-left: var(--border-thin) solid var(--color-line);
  color: var(--color-ink-soft);
  transition: color 0.18s ease, border-color 0.18s ease;
}
.toc-rail a:hover { color: var(--color-primary); }
.toc-rail a[aria-current] {
  color: var(--color-primary);
  border-left: var(--border-thick) solid var(--color-primary);
  font-weight: var(--weight-heading);
}
.section--deep .toc-rail a { color: color-mix(in srgb, var(--color-contrast-ink) 70%, transparent); }
.section--deep .toc-rail a[aria-current] { color: var(--color-contrast-accent); border-left-color: var(--color-contrast-accent); }

/* ---------- 6. 页头 ---------- */
.skip-link {
  position: absolute;
  left: var(--space-3);
  top: -120px;
  z-index: 200;
  padding: var(--space-1) var(--space-2);
  background-color: var(--color-primary);
  color: var(--color-primary-ink);
  font-size: var(--text-sm);
  letter-spacing: 0.1em;
  transition: top 0.18s ease;
}
.skip-link:focus { top: var(--space-2); }

.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 90;
  background-color: var(--color-surface);
  color: var(--color-ink);
  border-bottom: var(--border-thin) solid var(--color-line);
  transition: background-color 0.28s ease, border-color 0.28s ease, color 0.28s ease;
}
.site-header[data-state="overlay"][data-scrolled="false"] {
  background-color: transparent;
  border-bottom-color: transparent;
  color: var(--color-contrast-ink);
}

.site-header__inner {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  min-height: calc(var(--space-8) + var(--space-3));
}

.brand {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  flex: 0 0 auto;
}
.brand__mark {
  display: inline-block;
  writing-mode: vertical-rl;
  text-orientation: upright;
  height: var(--space-6);
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  font-weight: var(--weight-heading);
  line-height: 1.06;
  letter-spacing: 0.06em;
  color: var(--color-primary);
}
.brand__meta {
  display: block;
  max-width: 11em;
  font-size: var(--text-xs);
  line-height: 1.45;
  letter-spacing: 0.06em;
  color: var(--color-ink-muted);
}
.site-header[data-state="overlay"][data-scrolled="false"] .brand__mark { color: var(--color-contrast-accent); }
.site-header[data-state="overlay"][data-scrolled="false"] .brand__meta {
  color: var(--color-contrast-ink);
  opacity: 0.72;
}

.nav-toggle {
  display: none;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-1) var(--space-2);
  border: var(--border-thin) solid currentColor;
  border-radius: var(--radius-sm);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
}
.nav-toggle__bars { display: grid; gap: 4px; }
.nav-toggle__bar {
  display: block;
  width: 16px;
  height: var(--border-thin);
  background-color: currentColor;
  transition: transform 0.2s ease;
}
.nav-toggle[data-open] .nav-toggle__bar:first-child { transform: translateY(2.5px) rotate(45deg); }
.nav-toggle[data-open] .nav-toggle__bar:last-child { transform: translateY(-2.5px) rotate(-45deg); }

.site-nav { margin-left: auto; }
.site-nav__list {
  counter-reset: navidx;
  display: flex;
  align-items: center;
  gap: var(--space-3);
}
.site-nav__item::before { content: none; }
.site-nav__link {
  position: relative;
  display: block;
  padding: var(--space-1) 0;
  font-size: var(--text-sm);
  letter-spacing: 0.1em;
  white-space: nowrap;
  color: inherit;
}
.site-nav__link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: var(--border-thick);
  background-color: var(--color-primary);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 0.22s ease;
}
.site-nav__link:hover::after,
.site-nav__link[aria-current="page"]::after { transform: scaleX(1); }
.site-nav__link:hover,
.site-nav__link[aria-current="page"] { color: var(--color-primary); }
.site-header[data-state="overlay"][data-scrolled="false"] .site-nav__link::after { background-color: var(--color-contrast-accent); }
.site-header[data-state="overlay"][data-scrolled="false"] .site-nav__link:hover,
.site-header[data-state="overlay"][data-scrolled="false"] .site-nav__link[aria-current="page"] { color: var(--color-contrast-accent); }

.header-aside {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  margin-left: var(--space-4);
  flex: 0 0 auto;
}
.round-chip {
  display: inline-flex;
  align-items: stretch;
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
  overflow: hidden;
}
.round-chip__key {
  padding: 3px var(--space-1);
  background-color: var(--color-primary);
  color: var(--color-primary-ink);
  font-size: var(--text-xs);
  letter-spacing: 0.12em;
  line-height: 1.6;
}
.round-chip__val {
  padding: 3px var(--space-1);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  line-height: 1.6;
  font-variant-numeric: tabular-nums;
}
.header-cta {
  padding: var(--space-1) var(--space-2);
  border: var(--border-thin) solid var(--color-ink);
  border-radius: var(--radius-sm);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  line-height: 1.6;
  transition: background-color 0.18s ease, color 0.18s ease, border-color 0.18s ease;
}
.header-cta:hover {
  background-color: var(--color-primary);
  border-color: var(--color-primary);
  color: var(--color-primary-ink);
}
.site-header[data-state="overlay"][data-scrolled="false"] .round-chip { border-color: var(--color-contrast-line); }
.site-header[data-state="overlay"][data-scrolled="false"] .round-chip__key {
  background-color: var(--color-contrast-accent);
  color: var(--color-contrast-surface);
}
.site-header[data-state="overlay"][data-scrolled="false"] .round-chip__val { color: var(--color-contrast-ink); }
.site-header[data-state="overlay"][data-scrolled="false"] .header-cta {
  border-color: var(--color-contrast-accent);
  color: var(--color-contrast-accent);
}
.site-header[data-state="overlay"][data-scrolled="false"] .header-cta:hover {
  background-color: var(--color-contrast-accent);
  color: var(--color-contrast-surface);
}

.scroll-progress {
  position: absolute;
  left: 0;
  right: 0;
  bottom: -1px;
  height: var(--border-thick);
  background-color: var(--color-primary);
  transform: scaleX(0);
  transform-origin: 0 50%;
  pointer-events: none;
}

/* ---------- 7. 页脚 ---------- */
.site-footer {
  position: relative;
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}
.site-footer::before {
  content: "";
  display: block;
  height: 10px;
  border-top: var(--border-thin) solid var(--color-contrast-line);
  border-bottom: var(--border-thick) solid var(--color-primary);
  background-image: repeating-linear-gradient(90deg, var(--color-contrast-line) 0 1px, transparent 1px 10px);
}

.footer-top {
  display: grid;
  grid-template-columns: minmax(0, 1.2fr) minmax(0, 1fr);
  gap: var(--space-6);
  padding-block: var(--space-8) var(--space-6);
  border-bottom: var(--border-thin) solid var(--color-contrast-line);
}
.footer-brand__name {
  font-family: var(--font-heading);
  font-size: var(--text-xl);
  font-weight: var(--weight-heading);
  letter-spacing: 0.06em;
  color: var(--color-contrast-ink);
}
.footer-brand__note {
  margin-top: var(--space-2);
  max-width: 34ch;
  font-size: var(--text-sm);
  line-height: 1.7;
  color: color-mix(in srgb, var(--color-contrast-ink) 68%, transparent);
}
.footer-nav__list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: var(--space-2) var(--space-4);
}
.footer-nav a {
  display: block;
  padding-block: 2px;
  font-size: var(--text-sm);
  letter-spacing: 0.1em;
  color: color-mix(in srgb, var(--color-contrast-ink) 82%, transparent);
  border-bottom: var(--border-thin) solid transparent;
  transition: color 0.18s ease, border-color 0.18s ease;
}
.footer-nav a:hover {
  color: var(--color-contrast-accent);
  border-bottom-color: var(--color-contrast-accent);
}

.footer-contact {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2) var(--space-6);
  padding-block: var(--space-4);
  border-bottom: var(--border-thin) solid var(--color-contrast-line);
  font-size: var(--text-sm);
  color: color-mix(in srgb, var(--color-contrast-ink) 78%, transparent);
}
.footer-contact__item { display: inline-flex; gap: var(--space-1); }
.footer-contact__key {
  color: var(--color-contrast-accent);
  letter-spacing: 0.12em;
  font-size: var(--text-xs);
  align-self: center;
  padding-right: 2px;
  border-right: var(--border-thin) solid var(--color-contrast-line);
}

.footer-word {
  margin-block: var(--space-4) var(--space-2);
  font-family: var(--font-heading);
  font-size: var(--text-display);
  font-weight: var(--weight-heading);
  line-height: 0.94;
  letter-spacing: -0.01em;
  text-align: center;
  white-space: nowrap;
  overflow: hidden;
  color: var(--color-contrast-line);
  user-select: none;
}

.footer-legal {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: var(--space-2) var(--space-4);
  padding-block: var(--space-3) var(--space-4);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  color: color-mix(in srgb, var(--color-contrast-ink) 58%, transparent);
}

.to-top {
  position: fixed;
  right: var(--space-3);
  bottom: var(--space-3);
  z-index: 80;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: var(--space-1) var(--space-2);
  border: var(--border-thin) solid var(--color-contrast-line);
  border-radius: var(--radius-sm);
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  opacity: 0;
  visibility: hidden;
  transform: translateY(8px);
  transition: opacity 0.24s ease, transform 0.24s ease, visibility 0.24s ease, color 0.18s ease;
}
.to-top[data-visible="true"] {
  opacity: 1;
  visibility: visible;
  transform: none;
}
.to-top:hover { color: var(--color-contrast-accent); }

/* ---------- 8. 响应式 ---------- */
@media (max-width: 960px) {
  .shell { padding-inline: var(--space-3); }

  .nav-toggle {
    display: inline-flex;
    order: 3;
    margin-left: var(--space-2);
  }
  .header-aside {
    order: 2;
    margin-left: auto;
    gap: var(--space-2);
  }
  .header-cta { display: none; }

  .site-nav {
    position: fixed;
    top: calc(var(--space-8) + var(--space-3));
    left: 0;
    right: 0;
    max-height: calc(100vh - 88px);
    overflow-y: auto;
    margin-left: 0;
    padding: var(--space-2) var(--space-3) var(--space-4);
    background-color: var(--color-surface);
    border-bottom: var(--border-thick) solid var(--color-primary);
    display: none;
  }
  .site-nav[data-open] { display: block; }
  .site-nav__list { display: block; }
  .site-nav__item {
    counter-increment: navidx;
    display: flex;
    align-items: baseline;
    gap: var(--space-2);
    border-bottom: var(--border-thin) solid var(--color-line);
  }
  .site-nav__item::before {
    content: counter(navidx, decimal-leading-zero);
    min-width: 2.4em;
    font-family: var(--font-mono);
    font-size: var(--text-xs);
    letter-spacing: 0.06em;
    color: var(--color-primary);
  }
  .site-nav__link {
    flex: 1;
    padding-block: var(--space-2);
    font-size: var(--text-base);
  }
  .site-nav__link::after { display: none; }
  .site-nav__link:hover,
  .site-nav__link[aria-current="page"] { color: var(--color-primary); }

  .grid--3, .grid--4 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .footer-top { grid-template-columns: minmax(0, 1fr); gap: var(--space-4); }
  .toc-rail { position: static; }
}

@media (max-width: 640px) {
  .section { padding-block: var(--space-8); }
  .section--lg { padding-block: var(--space-8); }

  .grid--2, .grid--3, .grid--4 { grid-template-columns: minmax(0, 1fr); }

  .brand__meta { max-width: 7em; }
  .footer-nav__list { grid-template-columns: minmax(0, 1fr); }
  .footer-contact { flex-direction: column; gap: var(--space-2); }
  .footer-legal { flex-direction: column; }
  .footer-word { white-space: normal; }

  .btn { width: 100%; justify-content: center; }
}

/* ---------- 9. 可访问性与动效降级 ---------- */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
  }
  .scroll-progress { transition: none; }
}