:root {
  --color-surface: #f8f7f7;
  --color-surface-alt: #f0eeee;
  --color-surface-deep: #e4e2e1;
  --color-ink: #50453f;
  --color-ink-soft: #766860;
  --color-ink-muted: #8b7d74;
  --color-line: #dad7d6;
  --color-primary: #ab6235;
  --color-primary-ink: #ffffff;
  --color-primary-soft: #ede2dc;
  --color-accent: #b0631c;
  --color-accent-ink: #ffffff;
  --color-highlight: #ebdcd0;
  --color-focus: #ac5b11;
  --color-contrast-surface: #1d1612;
  --color-contrast-ink: #e7e5e4;
  --color-contrast-line: #494440;
  --color-contrast-accent: #dc7c23;
  --overlay-scrim: linear-gradient(180deg, rgba(29, 22, 18, 0.35) 0%, rgba(29, 22, 18, 0.72) 55%, rgba(29, 22, 18, 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: 10.4px;
  --text-sm: 13.9px;
  --text-base: 16px;
  --text-lg: 21.3px;
  --text-xl: 28.4px;
  --text-2xl: 37.9px;
  --text-3xl: 50.5px;
  --text-4xl: 67.3px;
  --text-display: clamp(46px, 9.5vw, 122px);
  --text-figure: clamp(39px, 6.9vw, 88px);
  --weight-heading: 729;
  --weight-body: 400;
  --leading-body: 1.69;
  --leading-heading: 1.23;
  --tracking-heading: 0.017em;
  --radius-sm: 1px;
  --radius-md: 2px;
  --radius-lg: 2px;
  --radius-pill: 2px;
  --border-thin: 1px;
  --border-thick: 2px;
  --shadow-1: 0 1px 0 rgba(80, 69, 63, 0.12);
  --shadow-2: 0 2px 0 rgba(80, 69, 63, 0.18);
  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 32px;
  --space-6: 48px;
  --space-8: 64px;
  --container: 1040px;
  --measure: 68ch;
  --gutter: 32px;
  --section-y: 77px;
  --section-y-lg: 108px;
}

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

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: 120px;
}

body {
  margin: 0;
  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: 0.018em;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

img, svg, video { display: block; max-width: 100%; height: auto; }
button, input, select, textarea { font: inherit; color: inherit; }
ul, ol { margin: 0; padding: 0; }
li { list-style: none; }

#main-content { scroll-margin-top: 120px; }

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

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

/* ==========================================================================
   2. 中文排版
   ========================================================================== */
h1, h2, h3, h4, h5 {
  margin: 0 0 var(--space-2);
  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-3xl); }
h2 { font-size: var(--text-2xl); }
h3 { font-size: var(--text-xl); }
h4 { font-size: var(--text-lg); }
h5 { font-size: var(--text-base); }

p { margin: 0 0 var(--space-2); }
p:last-child { margin-bottom: 0; }

strong, b { font-weight: 700; color: var(--color-ink); }

small { font-size: var(--text-sm); }

a {
  color: var(--color-primary);
  text-decoration: underline;
  text-decoration-thickness: var(--border-thin);
  text-underline-offset: 3px;
  transition: color 0.16s ease, text-decoration-thickness 0.16s ease;
}

a:hover { color: var(--color-accent); text-decoration-thickness: var(--border-thick); }

code, kbd, samp, .mono {
  font-family: var(--font-mono);
  font-size: 0.94em;
  letter-spacing: 0.04em;
}

/* ==========================================================================
   3. 布局工具
   ========================================================================== */
.container {
  width: 100%;
  max-width: var(--container);
  margin: 0 auto;
  padding-left: var(--space-3);
  padding-right: var(--space-3);
}

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

.page-section {
  padding-top: var(--section-y);
  padding-bottom: var(--section-y);
}

.page-section--lg {
  padding-top: var(--section-y-lg);
  padding-bottom: var(--section-y-lg);
}

.page-section--contrast {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}

.page-section--contrast h1,
.page-section--contrast h2,
.page-section--contrast h3,
.page-section--contrast h4,
.page-section--contrast strong { color: var(--color-contrast-ink); }

.page-section--contrast a { color: var(--color-contrast-accent); }

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

.rule {
  border: 0;
  border-top: 3px double var(--color-line);
  margin: var(--space-6) 0;
}

.rule--dot {
  border-top: var(--border-thin) dotted var(--color-line);
}

/* ==========================================================================
   4. 章节抬头 / 正文
   ========================================================================== */
.section-head {
  max-width: 760px;
  margin: 0 auto var(--space-6);
  text-align: center;
}

.section-head--left {
  margin-left: 0;
  margin-right: 0;
  text-align: left;
}

.section-kicker {
  display: inline-block;
  margin-bottom: var(--space-2);
  padding-bottom: 2px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.22em;
  color: var(--color-primary);
  border-bottom: 3px double var(--color-primary);
}

.page-section--contrast .section-kicker {
  color: var(--color-contrast-accent);
  border-bottom-color: var(--color-contrast-accent);
}

.section-title {
  margin: 0;
  font-size: var(--text-2xl);
}

.prose {
  max-width: var(--measure);
  font-size: var(--text-base);
  line-height: var(--leading-body);
  color: var(--color-ink);
}

.prose p { margin-bottom: var(--space-3); }
.prose h2 { margin-top: var(--space-6); font-size: var(--text-xl); }
.prose h3 { margin-top: var(--space-4); font-size: var(--text-lg); }

.display-title {
  margin: 0;
  font-family: var(--font-heading);
  font-size: var(--text-display);
  font-weight: var(--weight-heading);
  line-height: 1.08;
  letter-spacing: var(--tracking-heading);
  color: var(--color-ink);
}

.figure-number {
  display: block;
  font-family: var(--font-heading);
  font-size: var(--text-figure);
  font-weight: var(--weight-heading);
  line-height: 1.04;
  letter-spacing: -0.012em;
  color: var(--color-accent);
}

.figure-number--on-dark { color: var(--color-contrast-accent); }

[data-figure] {
  color: var(--color-ink-muted);
  transition: color 0.4s ease;
}

[data-figure].is-counted { color: var(--color-accent); }

.page-section--contrast [data-figure].is-counted { color: var(--color-contrast-accent); }

/* ==========================================================================
   5. 标签 / 说明牌 / 票据 / 面板
   ========================================================================== */
.tag {
  display: inline-block;
  padding: 2px 8px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.12em;
  color: var(--color-ink-soft);
  background-color: var(--color-surface);
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
}

.tag--primary {
  color: var(--color-primary);
  background-color: var(--color-primary-soft);
  border-color: var(--color-primary-soft);
}

.tag--accent {
  color: var(--color-accent-ink);
  background-color: var(--color-accent);
  border-color: var(--color-accent);
}

.plate {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: 3px 10px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  color: var(--color-ink-soft);
  background-color: var(--color-surface-alt);
  border: var(--border-thin) solid var(--color-line);
  border-left: var(--border-thick) solid var(--color-primary);
  border-radius: var(--radius-sm);
}

.plate--accent {
  color: var(--color-accent);
  border-left-color: var(--color-accent);
  background-color: var(--color-surface);
}

.ticket {
  position: relative;
  padding: calc(var(--space-3) + 6px) var(--space-3) var(--space-3);
  background-color: var(--color-surface-alt);
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
}

.ticket::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background-image: repeating-linear-gradient(90deg, var(--color-primary) 0 10px, transparent 10px 20px);
  opacity: 0.7;
}

.panel {
  padding: var(--space-3);
  background-color: var(--color-surface);
  border: 3px double var(--color-line);
  border-radius: var(--radius-md);
}

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

.panel__label {
  display: block;
  margin-bottom: var(--space-1);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  color: var(--color-ink-muted);
}

/* ==========================================================================
   6. 按钮
   ========================================================================== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-1);
  padding: 11px 20px;
  font-family: var(--font-body);
  font-size: var(--text-sm);
  letter-spacing: 0.08em;
  line-height: 1.2;
  text-decoration: none;
  color: var(--color-ink);
  background-color: transparent;
  border: var(--border-thin) solid var(--color-ink);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: background-color 0.18s ease, color 0.18s ease, border-color 0.18s ease;
}

.btn:hover {
  outline: 3px double var(--color-ink);
  outline-offset: -3px;
}

.btn--primary {
  color: var(--color-primary-ink);
  background-color: var(--color-primary);
  border-color: var(--color-primary);
}

.btn--primary:hover {
  color: var(--color-accent-ink);
  background-color: var(--color-accent);
  border-color: var(--color-accent);
  outline-color: var(--color-accent);
}

.btn--outline {
  color: var(--color-primary);
  background-color: transparent;
  border-color: var(--color-primary);
}

.btn--outline:hover {
  color: var(--color-accent);
  border-color: var(--color-accent);
  outline-color: var(--color-accent);
}

.page-section--contrast .btn {
  color: var(--color-contrast-ink);
  border-color: var(--color-contrast-line);
}

.page-section--contrast .btn:hover { outline-color: var(--color-contrast-accent); }

/* ==========================================================================
   7. 面包屑
   ========================================================================== */
.breadcrumb {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 6px;
  margin-bottom: var(--space-2);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: var(--color-ink-muted);
}

.breadcrumb__item { display: inline-flex; align-items: center; }

.breadcrumb__item::after {
  content: "/";
  margin-left: 6px;
  color: var(--color-line);
}

.breadcrumb__item:last-child::after { content: ""; }

.breadcrumb a {
  color: var(--color-ink-soft);
  text-decoration: none;
  border-bottom: var(--border-thin) dotted var(--color-line);
}

.breadcrumb a:hover { color: var(--color-accent); border-bottom-style: double; }

/* ==========================================================================
   8. 图片容器
   ========================================================================== */
.media-frame {
  position: relative;
  overflow: hidden;
  isolation: isolate;
  background-color: var(--color-surface-deep);
  border: 3px double var(--color-line);
  border-radius: var(--radius-md);
}

.media-frame--wide { aspect-ratio: 16 / 9; }
.media-frame--square { aspect-ratio: 1 / 1; }
.media-frame--tall { aspect-ratio: 3 / 4; }

.media-frame__img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.media-frame__scrim {
  position: absolute;
  inset: 0;
  background-image: var(--overlay-scrim);
  pointer-events: none;
}

.media-frame__caption {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  z-index: 2;
  padding: var(--space-3);
  color: var(--color-contrast-ink);
}

.media-frame__caption h3,
.media-frame__caption p { color: var(--color-contrast-ink); }

.media-frame__caption .plate {
  background-color: rgba(29, 22, 18, 0.6);
  border-color: var(--color-contrast-line);
  color: var(--color-contrast-ink);
}

/* ==========================================================================
   9. 章节索引
   ========================================================================== */
.chapter-index {
  position: sticky;
  top: 116px;
  align-self: start;
}

.chapter-index__title {
  margin: 0 0 var(--space-2);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.2em;
  color: var(--color-ink-muted);
}

.chapter-index__list {
  border-left: 3px double var(--color-line);
}

.index-link {
  display: block;
  margin-left: -3px;
  padding: 7px 0 7px 14px;
  font-size: var(--text-sm);
  color: var(--color-ink-muted);
  text-decoration: none;
  border-left: 3px solid transparent;
  transition: color 0.16s ease, border-color 0.16s ease, background-color 0.16s ease;
}

.index-link:hover {
  color: var(--color-ink);
  background-color: var(--color-surface-alt);
  border-left-style: double;
  border-left-color: var(--color-line);
}

.index-link[aria-current="true"] {
  color: var(--color-accent);
  border-left-color: var(--color-accent);
  font-weight: 700;
}

/* ==========================================================================
   10. 页头
   ========================================================================== */
.site-header {
  position: sticky;
  top: 0;
  z-index: 60;
  background-color: var(--color-surface);
  border-bottom: 3px double var(--color-line);
}

.site-header::after {
  content: "";
  display: block;
  height: 3px;
  background-image: repeating-linear-gradient(90deg, var(--color-accent) 0 8px, transparent 8px 18px);
  opacity: 0.5;
}

.site-header__inner {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  width: 100%;
  max-width: var(--container);
  margin: 0 auto;
  padding: 11px var(--space-3);
}

.skip-link {
  position: absolute;
  left: var(--space-2);
  top: calc(-1 * var(--space-8));
  z-index: 100;
  padding: 10px 16px;
  font-size: var(--text-sm);
  letter-spacing: 0.08em;
  text-decoration: none;
  color: var(--color-contrast-ink);
  background-color: var(--color-contrast-surface);
  border: 3px double var(--color-contrast-line);
  border-radius: var(--radius-sm);
  transition: top 0.18s ease;
}

.skip-link:focus { top: var(--space-2); color: var(--color-contrast-ink); }

.brand {
  display: flex;
  align-items: baseline;
  gap: var(--space-2);
  min-width: 0;
}

.brand__link { text-decoration: none; }

.brand__mark {
  display: inline-block;
  padding-bottom: 1px;
  font-family: var(--font-heading);
  font-size: var(--text-xl);
  font-weight: var(--weight-heading);
  letter-spacing: 0.06em;
  line-height: 1.1;
  color: var(--color-ink);
  border-bottom: 3px double var(--color-primary);
}

.brand__link:hover .brand__mark { color: var(--color-primary); border-bottom-color: var(--color-accent); }

.brand__meta {
  margin: 0;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  color: var(--color-ink-muted);
  white-space: nowrap;
}

.nav-toggle {
  display: none;
  align-items: center;
  gap: var(--space-1);
  margin-left: auto;
  padding: 8px 12px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  color: var(--color-ink);
  background-color: var(--color-surface-alt);
  border: 3px double var(--color-line);
  border-radius: var(--radius-sm);
  cursor: pointer;
}

.nav-toggle__mark {
  display: block;
  width: 14px;
  height: 8px;
  border-top: var(--border-thick) solid var(--color-ink);
  border-bottom: var(--border-thick) solid var(--color-ink);
}

.site-header[data-open="true"] .nav-toggle {
  color: var(--color-accent);
  background-color: var(--color-primary-soft);
  border-color: var(--color-accent);
}

.site-header[data-open="true"] .nav-toggle__mark {
  border-top-color: var(--color-accent);
  border-bottom-color: var(--color-accent);
}

.primary-nav {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  margin-left: auto;
}

.nav-list {
  display: flex;
  align-items: center;
  gap: 2px;
}

.nav-list__item { margin: 0; }

.nav-link {
  position: relative;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 7px 9px;
  font-size: var(--text-sm);
  letter-spacing: 0.06em;
  color: var(--color-ink-soft);
  text-decoration: none;
  border-radius: var(--radius-sm);
  transition: background-color 0.16s ease, color 0.16s ease;
}

.nav-link::before {
  content: "";
  flex: none;
  width: 4px;
  height: 4px;
  background-color: var(--color-surface-deep);
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
}

.nav-link:hover {
  color: var(--color-ink);
  background-color: var(--color-surface-alt);
  outline: 3px double var(--color-line);
  outline-offset: -3px;
}

.nav-link[aria-current="page"] {
  color: var(--color-ink);
  background-color: var(--color-primary-soft);
}

.nav-link[aria-current="page"]::before {
  background-color: var(--color-accent);
  border-color: var(--color-accent);
}

.nav-link[aria-current="page"]::after {
  content: "";
  position: absolute;
  left: 9px;
  right: 9px;
  bottom: -1px;
  border-bottom: 3px double var(--color-accent);
}

.nav-cta {
  display: inline-flex;
  align-items: center;
  padding: 9px 14px;
  font-size: var(--text-sm);
  letter-spacing: 0.08em;
  text-decoration: none;
  color: var(--color-primary-ink);
  background-color: var(--color-primary);
  border: var(--border-thin) solid var(--color-primary);
  border-radius: var(--radius-sm);
  transition: background-color 0.18s ease, border-color 0.18s ease, color 0.18s ease;
}

.nav-cta:hover {
  color: var(--color-accent-ink);
  background-color: var(--color-accent);
  border-color: var(--color-accent);
}

/* ==========================================================================
   11. 页脚
   ========================================================================== */
.site-footer {
  position: relative;
  padding: var(--space-8) 0 var(--space-4);
  color: var(--color-contrast-ink);
  background-color: var(--color-contrast-surface);
  border-top: 3px double var(--color-contrast-line);
}

.site-footer a {
  color: var(--color-contrast-ink);
  text-decoration: none;
  border-bottom: var(--border-thin) solid var(--color-contrast-line);
  transition: color 0.16s ease, border-color 0.16s ease;
}

.site-footer a:hover {
  color: var(--color-contrast-accent);
  border-bottom: 3px double var(--color-contrast-accent);
}

.site-footer__inner { position: relative; }

.site-footer__lead {
  display: grid;
  gap: var(--space-1);
  padding-bottom: var(--space-4);
}

.site-footer__line {
  margin: 0;
  font-family: var(--font-heading);
  font-size: var(--text-lg);
  font-weight: var(--weight-heading);
  line-height: var(--leading-heading);
  letter-spacing: var(--tracking-heading);
  color: var(--color-contrast-ink);
}

.footer-index {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: var(--space-4);
  padding-top: var(--space-4);
  border-top: 3px double var(--color-contrast-line);
}

.footer-col__title {
  margin: 0 0 var(--space-2);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  font-weight: 400;
  letter-spacing: 0.2em;
  color: color-mix(in srgb, var(--color-contrast-ink) 62%, transparent);
}

.footer-col__list {
  display: grid;
  gap: var(--space-1);
  font-size: var(--text-sm);
}

.footer-col__plain {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  color: color-mix(in srgb, var(--color-contrast-ink) 72%, transparent);
}

.footer-brand {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  margin: var(--space-6) 0 0;
  padding-top: var(--space-4);
  font-family: var(--font-heading);
  font-size: clamp(calc(var(--text-2xl) * 1.15), 10vw, calc(var(--text-4xl) * 1.75));
  font-weight: var(--weight-heading);
  line-height: 0.95;
  letter-spacing: 0;
  color: var(--color-contrast-ink);
  border-top: 3px double var(--color-contrast-line);
  user-select: none;
}

.footer-brand span { display: block; }

.footer-base {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-1) var(--space-4);
  margin-top: var(--space-4);
  padding-top: var(--space-2);
  border-top: var(--border-thin) dotted var(--color-contrast-line);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: color-mix(in srgb, var(--color-contrast-ink) 66%, transparent);
}

.footer-base__item { margin: 0; }

/* ==========================================================================
   12. 返回顶部
   ========================================================================== */
.back-to-top {
  position: fixed;
  right: var(--space-3);
  bottom: var(--space-3);
  z-index: 70;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 10px 14px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  color: var(--color-ink);
  background-color: var(--color-surface);
  border: 3px double var(--color-line);
  border-radius: var(--radius-sm);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(8px);
  transition: opacity 0.24s ease, transform 0.24s ease, visibility 0.24s linear;
}

.back-to-top::before {
  content: "";
  width: 5px;
  height: 5px;
  background-color: var(--color-accent);
  border-radius: var(--radius-sm);
}

.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top:hover { outline: 3px double var(--color-accent); outline-offset: -3px; }

/* ==========================================================================
   13. 渐显
   ========================================================================== */
[data-reveal] { transition: opacity 0.24s ease, transform 0.24s ease; }
[data-reveal].is-pending { opacity: 0; transform: translateY(8px); }
[data-reveal].is-visible { opacity: 1; transform: translateY(0); }

/* ==========================================================================
   14. 响应式
   ========================================================================== */
@media (max-width: 900px) {
  .grid--3,
  .grid--4 { grid-template-columns: repeat(2, minmax(0, 1fr)); }

  .footer-index { grid-template-columns: repeat(2, minmax(0, 1fr)); gap: var(--space-3); }
}

@media (max-width: 880px) {
  .site-header__inner {
    position: relative;
    flex-wrap: wrap;
    gap: var(--space-2);
    padding: 10px var(--space-3) 12px;
  }

  .nav-toggle { display: inline-flex; }

  .primary-nav {
    order: 3;
    flex-basis: 100%;
    width: 100%;
    display: none;
    flex-direction: column;
    align-items: stretch;
    gap: var(--space-2);
    margin-left: 0;
    padding-top: var(--space-2);
    border-top: 3px double var(--color-line);
  }

  .site-header[data-open="true"] .primary-nav { display: flex; }

  .nav-list {
    flex-direction: column;
    align-items: stretch;
    gap: 0;
  }

  .nav-link {
    padding: 11px 8px;
    font-size: var(--text-base);
    border-bottom: var(--border-thin) dotted var(--color-line);
    border-radius: 0;
  }

  .nav-link:hover { outline-offset: -1px; }

  .nav-link[aria-current="page"] {
    background-color: var(--color-primary-soft);
    border-bottom: 3px double var(--color-accent);
  }

  .nav-link[aria-current="page"]::after { display: none; }

  .nav-cta { justify-content: center; padding: 13px 16px; font-size: var(--text-base); }

  .chapter-index { position: static; }
}

@media (max-width: 700px) {
  .grid--2,
  .grid--3,
  .grid--4 { grid-template-columns: minmax(0, 1fr); }

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

  :root { --gutter: 20px; }
}

@media (max-width: 560px) {
  .brand {
    flex-direction: column;
    align-items: flex-start;
    gap: 0;
  }

  .brand__meta { white-space: normal; }

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

  .footer-base { flex-direction: column; gap: var(--space-1); }

  .back-to-top { right: var(--space-2); bottom: var(--space-2); }
}

/* ==========================================================================
   15. 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;
  }

  [data-reveal],
  [data-reveal].is-pending {
    opacity: 1;
    transform: none;
  }

  .back-to-top { transform: none; }
  .skip-link { transition: none; }
}