:root {
  --color-surface: #fefefe;
  --color-surface-alt: #f5f5f5;
  --color-surface-deep: #e8e9e8;
  --color-ink: #494c43;
  --color-ink-soft: #6d7066;
  --color-ink-muted: #82857a;
  --color-line: #dddedc;
  --color-primary: #70775f;
  --color-primary-ink: #ffffff;
  --color-primary-soft: #eaebe8;
  --color-accent: #618014;
  --color-accent-ink: #ffffff;
  --color-highlight: #e2e7d4;
  --color-focus: #5e7e0c;
  --color-contrast-surface: #191a17;
  --color-contrast-ink: #e6e7e4;
  --color-contrast-line: #464744;
  --color-contrast-accent: #a8dc23;
  --overlay-scrim: linear-gradient(180deg, rgba(25, 26, 23, 0.35) 0%, rgba(25, 26, 23, 0.72) 55%, rgba(25, 26, 23, 0.92) 100%);
  --font-heading: STZhongsong, "Source Han Serif SC", "Songti SC", SimSun, serif;
  --font-body: "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-mono: ui-monospace, Menlo, Consolas, monospace;
  --text-xs: 9.5px;
  --text-sm: 13.5px;
  --text-base: 16px;
  --text-lg: 22.6px;
  --text-xl: 32.0px;
  --text-2xl: 45.2px;
  --text-3xl: 64.0px;
  --text-4xl: 90.4px;
  --text-display: clamp(43px, 8.9vw, 114px);
  --text-figure: clamp(36px, 6.4vw, 82px);
  --weight-heading: 432;
  --weight-body: 400;
  --leading-body: 1.87;
  --leading-heading: 1.25;
  --tracking-heading: 0.038em;
  --radius-sm: 0px;
  --radius-md: 0px;
  --radius-lg: 0px;
  --radius-pill: 0px;
  --border-thin: 1px;
  --border-thick: 1px;
  --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: 1280px;
  --measure: 66ch;
  --gutter: 24px;
  --section-y: 136px;
  --section-y-lg: 190px;
}

/* ============================================================
   1. Reset
   ============================================================ */
*,
*::before,
*::after { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: 104px;
}

body,
h1, h2, h3, h4, h5, h6,
p, ul, ol, li, figure, figcaption,
blockquote, dl, dt, dd, fieldset, legend {
  margin: 0;
  padding: 0;
}

ul, ol { list-style: none; }

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

button, input, select, textarea { font: inherit; color: inherit; }
button { background: none; border: 0; padding: 0; cursor: pointer; }
a { color: inherit; text-decoration: none; }
table { border-collapse: collapse; width: 100%; }
[hidden] { display: none !important; }

/* ============================================================
   2. 中文排版基线
   ============================================================ */
body {
  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;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  overflow-x: hidden;
}

h1, h2, h3, h4 {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  line-height: var(--leading-heading);
  letter-spacing: var(--tracking-heading);
  color: var(--color-ink);
  text-wrap: balance;
}
h1 { font-size: var(--text-3xl); }
h2 { font-size: var(--text-2xl); }
h3 { font-size: var(--text-xl); }
h4 { font-size: var(--text-lg); }

p { text-wrap: pretty; }
strong, b { font-weight: 600; }
small { font-size: var(--text-sm); }

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

:focus-visible {
  outline: 2px solid var(--color-focus);
  outline-offset: 3px;
}
:focus:not(:focus-visible) { outline: none; }

[id] { scroll-margin-top: 104px; }

/* ============================================================
   3. 布局容器与分区
   ============================================================ */
.container {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.section { padding-block: var(--section-y); }
.section--lg { padding-block: var(--section-y-lg); }
.section--tight { padding-block: var(--space-8); }
.section--alt { background-color: var(--color-surface-alt); }
.section--deep { background-color: var(--color-surface-deep); }

.grid-12 {
  display: grid;
  grid-template-columns: repeat(12, minmax(0, 1fr));
  gap: var(--gutter);
}

/* ============================================================
   4. 文字工具
   ============================================================ */
.display {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-display);
  line-height: 1.06;
  letter-spacing: var(--tracking-heading);
  text-wrap: balance;
}

.figure-num {
  font-family: var(--font-mono);
  font-size: var(--text-figure);
  font-weight: 400;
  line-height: 1;
  font-variant-numeric: tabular-nums;
  letter-spacing: -0.01em;
  color: var(--color-ink);
}

.title-xl {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-4xl);
  line-height: 1.08;
  letter-spacing: var(--tracking-heading);
}
.title-l {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-3xl);
  line-height: 1.12;
  letter-spacing: var(--tracking-heading);
}
.title-m {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-2xl);
  line-height: 1.2;
  letter-spacing: var(--tracking-heading);
}
.title-s {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-lg);
  line-height: 1.35;
  letter-spacing: var(--tracking-heading);
}

.lead {
  font-size: var(--text-lg);
  line-height: 1.6;
  color: var(--color-ink-soft);
}

.annotation {
  font-size: var(--text-sm);
  line-height: 1.75;
  letter-spacing: 0.02em;
  color: var(--color-ink-muted);
}

.mono {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  letter-spacing: 0.01em;
}

.measure { max-width: var(--measure); }

.rail {
  border-left: 4px solid var(--color-primary);
  padding-left: var(--space-3);
}
.rail--accent { border-left-color: var(--color-accent); }

/* ============================================================
   5. 状态标记
   ============================================================ */
.tag {
  display: inline-block;
  padding: 3px var(--space-1);
  background-color: var(--color-highlight);
  color: var(--color-ink);
  font-size: var(--text-sm);
  line-height: 1.4;
  letter-spacing: 0.02em;
}
.tag--state {
  background-color: var(--color-accent);
  color: var(--color-accent-ink);
}

.badge-period {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  line-height: 1.4;
  letter-spacing: 0.02em;
  color: var(--color-accent);
}

/* ============================================================
   6. 按钮与内联跳转
   ============================================================ */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  border: var(--border-thin) solid var(--color-ink-soft);
  background-color: transparent;
  color: var(--color-ink);
  font-size: var(--text-sm);
  line-height: 1.4;
  letter-spacing: 0.06em;
  transition: background-color 150ms ease, color 150ms ease, border-color 150ms ease;
}
.btn:hover {
  background-color: var(--color-primary-soft);
  border-color: var(--color-primary);
  color: var(--color-ink);
}
.btn--solid {
  background-color: var(--color-contrast-surface);
  border-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}
.btn--solid:hover {
  background-color: var(--color-accent);
  border-color: var(--color-accent);
  color: var(--color-accent-ink);
}

.link-rail {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding-bottom: 6px;
  border-bottom: var(--border-thin) solid var(--color-line);
  font-size: var(--text-sm);
  letter-spacing: 0.03em;
  color: var(--color-ink);
  transition: border-color 150ms ease, color 150ms ease;
}
.link-rail:hover {
  border-bottom-color: var(--color-accent);
  color: var(--color-accent);
}

/* ============================================================
   7. 路径指示（线段式）
   ============================================================ */
.path {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-2);
  padding-block: var(--space-3);
  border-bottom: var(--border-thin) solid var(--color-line);
  font-size: var(--text-sm);
  letter-spacing: 0.02em;
  color: var(--color-ink-muted);
}
.path__item {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
}
.path__item + .path__item::before {
  content: "";
  display: inline-block;
  width: 20px;
  height: var(--border-thin);
  background-color: var(--color-line);
}
.path a { color: var(--color-ink-soft); }
.path a:hover { color: var(--color-accent); }

/* ============================================================
   8. 区块标题行
   ============================================================ */
.section-head {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: var(--space-3);
  padding-bottom: var(--space-3);
  border-bottom: var(--border-thin) solid var(--color-line);
  margin-bottom: var(--space-6);
}
.section-head__title {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-2xl);
  line-height: var(--leading-heading);
  letter-spacing: var(--tracking-heading);
}
.section-head__note {
  margin-left: auto;
  font-size: var(--text-sm);
  line-height: 1.6;
  color: var(--color-ink-muted);
}

/* ============================================================
   9. 图片容器与展签
   ============================================================ */
.media { display: block; }

.media__frame {
  position: relative;
  overflow: hidden;
  background-color: var(--color-surface-deep);
  border-radius: var(--radius-md);
}
.media__frame > img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}
.media__frame--wide { aspect-ratio: 16 / 9; }
.media__frame--banner { aspect-ratio: 21 / 9; }
.media__frame--square { aspect-ratio: 1 / 1; }
.media__frame--tall { aspect-ratio: 4 / 5; }

.media__scrim {
  position: absolute;
  inset: 0;
  background: var(--overlay-scrim);
  pointer-events: none;
}
.media__overlay {
  position: absolute;
  inset: auto 0 0 0;
  z-index: 1;
  padding: var(--space-6);
  color: var(--color-contrast-ink);
}
.media__overlay .title-s,
.media__overlay .lead { color: var(--color-contrast-ink); }

.media__caption {
  margin-top: var(--space-2);
  padding-left: var(--space-3);
  border-left: var(--border-thin) solid var(--color-line);
  font-size: var(--text-sm);
  line-height: 1.75;
  letter-spacing: 0.02em;
  color: var(--color-ink-muted);
}

/* ============================================================
   10. 轨道图形基元（同心方环 / 放射细线 / 方形节点）
   ============================================================ */
.orbit-figure {
  position: relative;
  aspect-ratio: 1 / 1;
  border: var(--border-thin) solid var(--color-line);
  background-color: transparent;
  overflow: hidden;
}
.orbit-figure::before,
.orbit-figure::after {
  content: "";
  position: absolute;
  border: var(--border-thin) solid var(--color-line);
}
.orbit-figure::before { inset: 16%; }
.orbit-figure::after { inset: 34%; }

.orbit-figure__ray {
  position: absolute;
  left: 50%;
  top: 0;
  bottom: 0;
  width: var(--border-thin);
  background-color: var(--color-line);
}

.orbit-node {
  position: absolute;
  left: var(--node-x, 50%);
  top: var(--node-y, 50%);
  width: 7px;
  height: 7px;
  background-color: var(--color-primary);
  transform: translate(-50%, -50%);
}
.orbit-node--active { background-color: var(--color-accent); }

/* ============================================================
   11. 目录清单行
   ============================================================ */
.row-list { border-top: var(--border-thin) solid var(--color-line); }

.row {
  display: grid;
  grid-template-columns: 72px minmax(0, 1fr) minmax(0, 22ch);
  gap: var(--space-2) var(--space-6);
  align-items: baseline;
  padding: var(--space-4) 0;
  padding-left: calc(var(--space-1) + 3px);
  border-bottom: var(--border-thin) solid var(--color-line);
  border-left: var(--border-thin) solid transparent;
  transition: background-color 150ms ease, border-left-color 150ms ease;
}
.row:hover,
.row:focus-within {
  background-color: var(--color-primary-soft);
  border-left-width: 4px;
  border-left-color: var(--color-accent);
  padding-left: var(--space-1);
}

.row__index {
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  line-height: 1.6;
  color: var(--color-ink-muted);
  transition: color 150ms ease, letter-spacing 150ms ease;
}
.row:hover .row__index,
.row:focus-within .row__index {
  color: var(--color-accent);
  letter-spacing: 0.08em;
}

.row__title {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-lg);
  line-height: 1.35;
  letter-spacing: var(--tracking-heading);
  color: var(--color-ink);
}

.row__note {
  font-size: var(--text-sm);
  line-height: 1.75;
  color: var(--color-ink-soft);
}

/* ============================================================
   12. 折叠面板
   ============================================================ */
.collapse-list { border-top: var(--border-thin) solid var(--color-line); }

.collapse { border-bottom: var(--border-thin) solid var(--color-line); }

.collapse__trigger {
  display: flex;
  width: 100%;
  align-items: baseline;
  gap: var(--space-3);
  padding: var(--space-3) 0;
  text-align: left;
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-lg);
  line-height: 1.4;
  letter-spacing: var(--tracking-heading);
  color: var(--color-ink);
  transition: color 150ms ease;
}
.collapse__trigger:hover { color: var(--color-primary); }
.collapse__trigger::after {
  content: "＋";
  margin-left: auto;
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  color: var(--color-ink-muted);
}
.collapse__trigger[aria-expanded="true"]::after {
  content: "－";
  color: var(--color-accent);
}

.collapse__panel {
  padding-bottom: var(--space-4);
  max-width: var(--measure);
}

/* ============================================================
   13. 强对比区块（每页唯一）
   ============================================================ */
.contrast-block {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  padding: var(--space-8);
}
.contrast-block h1,
.contrast-block h2,
.contrast-block h3,
.contrast-block h4,
.contrast-block .title-s,
.contrast-block .title-m,
.contrast-block .lead {
  color: var(--color-contrast-ink);
}
.contrast-block .figure-num,
.contrast-block .badge-period { color: var(--color-contrast-accent); }
.contrast-block .annotation,
.contrast-block .row__note { color: color-mix(in srgb, var(--color-contrast-ink) 68%, var(--color-contrast-surface)); }
.contrast-block .row-list,
.contrast-block .collapse-list { border-top-color: var(--color-contrast-line); }
.contrast-block .row,
.contrast-block .collapse { border-bottom-color: var(--color-contrast-line); }
.contrast-block .row { border-left-color: transparent; }
.contrast-block .row:hover,
.contrast-block .row:focus-within {
  background-color: color-mix(in srgb, var(--color-contrast-ink) 8%, var(--color-contrast-surface));
  border-left-color: var(--color-contrast-accent);
}
.contrast-block .row__index { color: color-mix(in srgb, var(--color-contrast-ink) 55%, var(--color-contrast-surface)); }
.contrast-block .row:hover .row__index { color: var(--color-contrast-accent); }
.contrast-block .btn { border-color: var(--color-contrast-line); color: var(--color-contrast-ink); }
.contrast-block .btn:hover { background-color: var(--color-contrast-accent); border-color: var(--color-contrast-accent); color: var(--color-contrast-surface); }

/* ============================================================
   14. 页头
   ============================================================ */
.site-header {
  position: sticky;
  top: 0;
  z-index: 60;
  background-color: var(--color-surface);
  border-bottom: var(--border-thin) solid var(--color-line);
}

.site-header__inner {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: var(--space-2) var(--space-4);
  min-height: 88px;
  padding-block: var(--space-2);
}

.site-header__brand {
  grid-column: 1;
  grid-row: 1;
  min-width: 0;
}

.brand {
  display: block;
  padding-block: 4px;
}
.brand__word {
  display: block;
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-lg);
  line-height: 1.15;
  letter-spacing: var(--tracking-heading);
  color: var(--color-ink);
}
.brand__word::before {
  content: "";
  display: inline-block;
  width: 6px;
  height: 6px;
  margin-right: 10px;
  background-color: var(--color-primary);
  vertical-align: 0.32em;
}
.brand__caption {
  display: block;
  margin-top: 4px;
  padding-left: 16px;
  font-size: var(--text-sm);
  line-height: 1.5;
  letter-spacing: 0.02em;
  color: var(--color-ink-muted);
}
.brand__caption--note { color: color-mix(in srgb, var(--color-ink-muted) 78%, var(--color-surface)); }
.brand:hover .brand__word { color: var(--color-primary); }

.site-header__utility {
  grid-column: 2;
  grid-row: 1;
  justify-self: end;
  font-size: var(--text-sm);
}

.utility-link {
  color: var(--color-ink-soft);
  text-decoration: underline;
  text-decoration-color: var(--color-line);
  text-decoration-thickness: var(--border-thin);
  text-underline-offset: 6px;
  transition: color 150ms ease, text-decoration-color 150ms ease;
}
.utility-link:hover {
  color: var(--color-accent);
  text-decoration-color: var(--color-accent);
}

.site-nav {
  grid-column: 3;
  grid-row: 1;
}
.site-nav__list {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}
.site-nav__link {
  display: inline-block;
  padding-block: 6px;
  font-size: var(--text-sm);
  line-height: 1.5;
  letter-spacing: 0.03em;
  color: var(--color-ink-soft);
  text-decoration: underline;
  text-decoration-color: transparent;
  text-decoration-thickness: var(--border-thin);
  text-underline-offset: 7px;
  transition: color 150ms ease, text-decoration-color 150ms ease;
}
.site-nav__link:hover {
  color: var(--color-ink);
  text-decoration-color: var(--color-ink-muted);
}
.site-nav__link[aria-current="page"] {
  color: var(--color-ink);
  text-decoration-color: var(--color-accent);
}

.nav-toggle {
  grid-column: 3;
  grid-row: 1;
  justify-self: end;
  display: none;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  border: var(--border-thin) solid var(--color-line);
  color: var(--color-ink);
  transition: border-color 150ms ease, background-color 150ms ease;
}
.nav-toggle:hover { border-color: var(--color-primary); background-color: var(--color-primary-soft); }
.nav-toggle__bars {
  display: block;
  width: 18px;
}
.nav-toggle__bars span {
  display: block;
  height: var(--border-thin);
  background-color: currentColor;
}
.nav-toggle__bars span + span { margin-top: 5px; }

.scroll-progress {
  position: absolute;
  left: 0;
  bottom: -1px;
  height: var(--border-thin);
  width: 0;
  background-color: var(--color-accent);
}

.skip-link {
  position: fixed;
  top: -100px;
  left: var(--space-2);
  z-index: 200;
  padding: var(--space-2) var(--space-4);
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  font-size: var(--text-sm);
  letter-spacing: 0.03em;
  transition: top 150ms ease;
}
.skip-link:focus { top: var(--space-2); }

/* ============================================================
   15. 页脚
   ============================================================ */
.site-footer {
  background-color: var(--color-primary);
  color: var(--color-primary-ink);
}

.site-footer__inner {
  padding-block: var(--space-8) var(--space-6);
}

.site-footer__masthead {
  padding-bottom: var(--space-6);
  border-bottom: var(--border-thin) solid color-mix(in srgb, var(--color-primary-ink) 26%, var(--color-primary));
}
.site-footer__wordmark {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-xl);
  line-height: 1.2;
  letter-spacing: var(--tracking-heading);
  color: var(--color-primary-ink);
}
.site-footer__caption {
  margin-top: var(--space-2);
  font-size: var(--text-sm);
  line-height: 1.75;
  letter-spacing: 0.02em;
  color: color-mix(in srgb, var(--color-primary-ink) 76%, var(--color-primary));
}

.site-footer__columns {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-6) var(--space-8);
  padding-top: var(--space-6);
}

.footer-col__title {
  padding-bottom: var(--space-2);
  border-bottom: var(--border-thin) solid color-mix(in srgb, var(--color-primary-ink) 26%, var(--color-primary));
  font-family: var(--font-body);
  font-weight: 400;
  font-size: var(--text-sm);
  line-height: 1.5;
  letter-spacing: 0.14em;
  color: color-mix(in srgb, var(--color-primary-ink) 80%, var(--color-primary));
}

.footer-col__list {
  margin-top: var(--space-3);
}
.footer-col__list li {
  padding-block: var(--space-2);
  font-size: var(--text-sm);
  line-height: 1.7;
  letter-spacing: 0.02em;
}
.footer-col__list li + li {
  border-top: var(--border-thin) solid color-mix(in srgb, var(--color-primary-ink) 14%, var(--color-primary));
}

.footer-col__list a {
  color: var(--color-primary-ink);
  text-decoration: underline;
  text-decoration-color: color-mix(in srgb, var(--color-primary-ink) 32%, var(--color-primary));
  text-decoration-thickness: var(--border-thin);
  text-underline-offset: 5px;
  transition: text-decoration-color 150ms ease, color 150ms ease;
}
.footer-col__list a:hover { text-decoration-color: var(--color-primary-ink); }

.footer-col__text {
  color: color-mix(in srgb, var(--color-primary-ink) 82%, var(--color-primary));
  word-break: break-word;
}

.site-footer__base {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2) var(--space-6);
  justify-content: space-between;
  margin-top: var(--space-8);
  padding-top: var(--space-4);
  border-top: var(--border-thin) solid color-mix(in srgb, var(--color-primary-ink) 26%, var(--color-primary));
  font-size: var(--text-sm);
  line-height: 1.7;
  letter-spacing: 0.02em;
  color: color-mix(in srgb, var(--color-primary-ink) 80%, var(--color-primary));
}
.site-footer__base-note {
  color: color-mix(in srgb, var(--color-primary-ink) 68%, var(--color-primary));
}

/* ============================================================
   16. 无障碍辅助
   ============================================================ */
.visually-hidden {
  position: absolute !important;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  white-space: nowrap;
  border: 0;
}

/* ============================================================
   17. 响应式
   ============================================================ */
@media (max-width: 1100px) {
  .site-footer__columns { gap: var(--space-6) var(--space-6); }
}

@media (max-width: 1024px) {
  html { scroll-padding-top: 92px; }
  [id] { scroll-margin-top: 92px; }

  .site-header__inner {
    grid-template-columns: minmax(0, 1fr) auto;
    gap: var(--space-2) var(--space-3);
    min-height: 76px;
  }
  .site-header__brand { grid-column: 1; grid-row: 1; }
  .site-header__utility { display: none; }
  .nav-toggle { display: inline-flex; grid-column: 2; grid-row: 1; }
  .site-nav {
    grid-column: 1 / -1;
    grid-row: 2;
    display: none;
    width: 100%;
    padding-top: var(--space-2);
    border-top: var(--border-thin) solid var(--color-line);
  }
  .site-header[data-open] .site-nav { display: block; }
  .site-nav__list {
    flex-direction: column;
    align-items: stretch;
    gap: 0;
  }
  .site-nav__link {
    display: block;
    padding: var(--space-3) 0;
    padding-left: 2px;
    border-bottom: var(--border-thin) solid var(--color-line);
    font-size: var(--text-base);
    text-underline-offset: 9px;
  }
  .site-nav__list li:last-child .site-nav__link { border-bottom: 0; }

  .brand__caption--note { display: none; }

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

@media (max-width: 720px) {
  .section { padding-block: var(--space-8); }
  .section--lg { padding-block: var(--space-8); }
  .section--tight { padding-block: var(--space-6); }

  .grid-12 { grid-template-columns: repeat(6, minmax(0, 1fr)); }

  .display { line-height: 1.1; }
  .title-xl { font-size: var(--text-3xl); }
  .title-l { font-size: var(--text-2xl); }

  .row {
    grid-template-columns: 48px minmax(0, 1fr);
    gap: var(--space-2) var(--space-3);
    padding-block: var(--space-3);
  }
  .row__note { grid-column: 2; }

  .contrast-block { padding: var(--space-6) var(--space-3); }

  .site-footer__columns { grid-template-columns: minmax(0, 1fr); }
  .site-footer__inner { padding-block: var(--space-6) var(--space-4); }
  .site-footer__base { justify-content: flex-start; }

  .media__overlay { padding: var(--space-4); }
  .section-head__note { margin-left: 0; }
}

/* ============================================================
   18. 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-behavior: auto !important;
  }
}