:root {
  --color-surface: #f9f9f9;
  --color-surface-alt: #f0f0f0;
  --color-surface-deep: #e3e4e4;
  --color-ink: #41494e;
  --color-ink-soft: #647077;
  --color-ink-muted: #768289;
  --color-line: #d8d9da;
  --color-primary: #2d7caf;
  --color-primary-ink: #ffffff;
  --color-primary-soft: #dce8ef;
  --color-accent: #0a856f;
  --color-accent-ink: #ffffff;
  --color-highlight: #cee4e0;
  --color-focus: #037d68;
  --color-contrast-surface: #121b20;
  --color-contrast-ink: #e4e6e7;
  --color-contrast-line: #40484c;
  --color-contrast-accent: #12edc7;
  --overlay-scrim: linear-gradient(180deg, rgba(18, 27, 32, 0.35) 0%, rgba(18, 27, 32, 0.72) 55%, rgba(18, 27, 32, 0.92) 100%);
  --font-heading: "PingFang SC", "HarmonyOS Sans SC", "Microsoft YaHei", "Source Han Sans SC", sans-serif;
  --font-body: "PingFang SC", "HarmonyOS Sans SC", "Microsoft YaHei", "Source Han Sans SC", sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  --text-xs: 12.2px;
  --text-sm: 15.2px;
  --text-base: 17px;
  --text-lg: 21.2px;
  --text-xl: 26.6px;
  --text-2xl: 33.2px;
  --text-3xl: 41.5px;
  --text-4xl: 51.9px;
  --text-display: clamp(53px, 10.9vw, 139px);
  --text-figure: clamp(44px, 7.8vw, 100px);
  --weight-heading: 691;
  --weight-body: 400;
  --leading-body: 1.78;
  --leading-heading: 1.28;
  --tracking-heading: -0.005em;
  --radius-sm: 14px;
  --radius-md: 14px;
  --radius-lg: 15px;
  --radius-pill: 999px;
  --border-thin: 1px;
  --border-thick: 1px;
  --shadow-1: 0 6px 18px rgba(65, 73, 78, 0.08);
  --shadow-2: 0 18px 44px rgba(65, 73, 78, 0.14);
  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 32px;
  --space-6: 48px;
  --space-8: 64px;
  --container: 1120px;
  --measure: 73ch;
  --gutter: 32px;
  --section-y: 95px;
  --section-y-lg: 133px;
}

/* ============================================================
   1. RESET 与基础层
   ============================================================ */
*,
*::before,
*::after { box-sizing: border-box; }

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

body {
  margin: 0;
  min-height: 100vh;
  font-family: var(--font-body);
  font-size: var(--text-base);
  font-weight: var(--weight-body);
  line-height: var(--leading-body);
  color: var(--color-ink);
  background-color: var(--color-surface);
  background-image:
    radial-gradient(72% 52% at 6% -8%, color-mix(in srgb, var(--color-primary) 22%, transparent), transparent 64%),
    radial-gradient(58% 44% at 98% 0%, color-mix(in srgb, var(--color-accent) 16%, transparent), transparent 62%),
    radial-gradient(60% 40% at 50% 108%, color-mix(in srgb, var(--color-primary) 12%, transparent), transparent 68%);
  background-attachment: fixed;
  background-repeat: no-repeat;
  overflow-x: hidden;
}

h1, h2, h3, h4, h5, h6 {
  margin: 0;
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  line-height: var(--leading-heading);
  letter-spacing: var(--tracking-heading);
}

p { margin: 0 0 var(--space-3); }
p:last-child { margin-bottom: 0; }

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

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; }

strong, b { font-weight: 600; }

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

hr {
  border: 0;
  border-top: var(--border-thin) solid var(--color-line);
  margin: var(--space-6) 0;
}

:focus-visible {
  outline: 2px solid var(--color-focus);
  outline-offset: 3px;
  border-radius: 6px;
}

.site-header :focus-visible,
.site-footer :focus-visible,
.section--contrast :focus-visible,
.panel--contrast :focus-visible {
  outline-color: var(--color-contrast-accent);
}

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

/* ============================================================
   2. 可达性工具
   ============================================================ */
.visually-hidden {
  position: absolute !important;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  white-space: nowrap;
  border: 0;
}

.skip-link {
  position: fixed;
  top: -120px;
  left: var(--space-3);
  z-index: 200;
  padding: 10px 18px;
  font-size: var(--text-sm);
  font-family: var(--font-mono);
  letter-spacing: 0.08em;
  color: var(--color-contrast-ink);
  background: var(--color-contrast-surface);
  border: var(--border-thin) solid var(--color-contrast-accent);
  border-radius: var(--radius-sm);
  transition: top 0.2s ease;
}

.skip-link:focus {
  top: var(--space-3);
}

/* ============================================================
   3. 布局骨架
   ============================================================ */
.container {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.container--wide { max-width: calc(var(--container) + 160px); }

.section { padding-block: var(--section-y); }
.section--lg { padding-block: var(--section-y-lg); }
.section--tight { padding-block: var(--space-6); }
.section--flush { padding-block: var(--space-6); }

.section--contrast {
  background: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  position: relative;
  isolation: isolate;
}

.section--contrast::before {
  content: "";
  position: absolute;
  inset: 0;
  z-index: -1;
  background:
    radial-gradient(70% 60% at 12% 0%, color-mix(in srgb, var(--color-primary) 34%, transparent), transparent 66%),
    radial-gradient(56% 50% at 92% 90%, color-mix(in srgb, var(--color-accent) 24%, transparent), transparent 64%);
}

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

.section-head {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  justify-content: space-between;
  gap: var(--space-2) var(--space-4);
  margin-bottom: var(--space-6);
}

.stack > * + * { margin-top: var(--space-3); }

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

.col-2  { grid-column: span 12; }
.col-3  { grid-column: span 12; }
.col-4  { grid-column: span 12; }
.col-5  { grid-column: span 12; }
.col-6  { grid-column: span 12; }
.col-7  { grid-column: span 12; }
.col-8  { grid-column: span 12; }
.col-9  { grid-column: span 12; }
.col-10 { grid-column: span 12; }
.col-12 { grid-column: span 12; }

@media (min-width: 760px) {
  .col-2  { grid-column: span 6; }
  .col-3  { grid-column: span 6; }
  .col-4  { grid-column: span 6; }
  .col-5  { grid-column: span 6; }
  .col-6  { grid-column: span 6; }
  .col-7  { grid-column: span 8; }
  .col-8  { grid-column: span 8; }
  .col-9  { grid-column: span 10; }
  .col-10 { grid-column: span 12; }
}

@media (min-width: 1040px) {
  .col-2  { grid-column: span 2; }
  .col-3  { grid-column: span 3; }
  .col-4  { grid-column: span 4; }
  .col-5  { grid-column: span 5; }
  .col-6  { grid-column: span 6; }
  .col-7  { grid-column: span 7; }
  .col-8  { grid-column: span 8; }
  .col-9  { grid-column: span 9; }
  .col-10 { grid-column: span 10; }
}

/* ============================================================
   4. 玻璃面板与编号系统
   ============================================================ */
.panel {
  position: relative;
  padding: var(--space-4);
  border: var(--border-thin) solid color-mix(in srgb, var(--color-primary) 32%, var(--color-line));
  border-radius: var(--radius-lg);
  background: color-mix(in srgb, var(--color-surface) 74%, transparent);
  -webkit-backdrop-filter: blur(14px) saturate(130%);
  backdrop-filter: blur(14px) saturate(130%);
  box-shadow: var(--shadow-1);
}

.panel--deep {
  background: color-mix(in srgb, var(--color-surface-deep) 68%, transparent);
  border-color: color-mix(in srgb, var(--color-ink-soft) 26%, var(--color-line));
}

.panel--contrast {
  background: color-mix(in srgb, var(--color-contrast-surface) 82%, transparent);
  border-color: color-mix(in srgb, var(--color-contrast-ink) 20%, transparent);
  color: var(--color-contrast-ink);
  box-shadow: var(--shadow-2);
}

.panel--flush { padding: 0; }

.panel__head {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  justify-content: space-between;
  gap: var(--space-2);
  padding-bottom: var(--space-2);
  margin-bottom: var(--space-3);
  border-bottom: var(--border-thin) solid var(--color-line);
}

.panel--contrast .panel__head { border-bottom-color: var(--color-contrast-line); }

.section-label {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  margin: 0;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--color-ink-muted);
  transition: opacity 0.22s ease, color 0.22s ease;
}

.section-label__num {
  font-size: var(--text-sm);
  letter-spacing: 0.08em;
  color: var(--color-accent);
  padding-right: var(--space-2);
  border-right: var(--border-thin) solid color-mix(in srgb, var(--color-accent) 55%, transparent);
}

.section-label__text { white-space: nowrap; }

.section--contrast .section-label { color: color-mix(in srgb, var(--color-contrast-ink) 66%, transparent); }
.section--contrast .section-label__num {
  color: var(--color-contrast-accent);
  border-right-color: color-mix(in srgb, var(--color-contrast-accent) 55%, transparent);
}

[data-chapter] .section-label { opacity: 0.45; }
[data-chapter][data-active="true"] .section-label { opacity: 1; }
[data-chapter][data-active="true"] .section-label__num { color: var(--color-primary); }
.section--contrast[data-chapter][data-active="true"] .section-label__num { color: var(--color-contrast-accent); }

/* ============================================================
   5. 文字与展示级组件
   ============================================================ */
.display-title {
  font-size: var(--text-display);
  line-height: 0.94;
  letter-spacing: -0.022em;
  font-weight: var(--weight-heading);
}

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

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

.figure-label {
  display: block;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.18em;
  color: var(--color-ink-muted);
  margin-top: var(--space-1);
}

.section--contrast .figure-label { color: color-mix(in srgb, var(--color-contrast-ink) 62%, transparent); }

.lede {
  font-size: var(--text-lg);
  line-height: 1.6;
  color: var(--color-ink-soft);
  max-width: var(--measure);
}

.section--contrast .lede { color: color-mix(in srgb, var(--color-contrast-ink) 82%, transparent); }

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

.prose h2 {
  font-size: var(--text-2xl);
  margin: var(--space-8) 0 var(--space-3);
}

.prose h3 {
  font-size: var(--text-xl);
  margin: var(--space-6) 0 var(--space-2);
}

.prose p { margin-bottom: var(--space-3); }

.prose ul,
.prose ol {
  margin: 0 0 var(--space-3);
  padding-left: 1.4em;
  list-style: disc;
}

.prose ol { list-style: decimal; }

.prose li { margin-bottom: var(--space-1); }

.prose a {
  color: var(--color-primary);
  border-bottom: var(--border-thin) solid color-mix(in srgb, var(--color-primary) 45%, transparent);
  transition: border-color 0.2s ease, color 0.2s ease;
}

.prose a:hover { border-bottom-color: var(--color-accent); color: var(--color-accent); }

.prose blockquote {
  margin: var(--space-4) 0;
  padding: var(--space-2) var(--space-3);
  border-left: 2px solid var(--color-accent);
  background: color-mix(in srgb, var(--color-primary-soft) 55%, transparent);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  color: var(--color-ink-soft);
}

.highlight {
  background: linear-gradient(transparent 58%, var(--color-highlight) 58%);
  padding: 0 0.14em;
  color: inherit;
}

.underline-accent {
  border-bottom: 2px solid var(--color-accent);
  padding-bottom: 1px;
}

/* ============================================================
   6. 按钮族
   ============================================================ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-1);
  padding: 11px 22px;
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  font-weight: var(--weight-heading);
  letter-spacing: 0.06em;
  line-height: 1.2;
  border: var(--border-thin) solid transparent;
  border-radius: var(--radius-pill);
  transition: background-color 0.2s ease, border-color 0.2s ease, color 0.2s ease, transform 0.2s ease;
}

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

.btn--primary:hover { background: color-mix(in srgb, var(--color-primary) 82%, var(--color-contrast-surface)); }

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

.btn--accent:hover { background: color-mix(in srgb, var(--color-accent) 82%, var(--color-contrast-surface)); }

.btn--ghost {
  background: color-mix(in srgb, var(--color-surface) 62%, transparent);
  border-color: color-mix(in srgb, var(--color-primary) 42%, var(--color-line));
  color: var(--color-ink);
  -webkit-backdrop-filter: blur(8px);
  backdrop-filter: blur(8px);
}

.btn--ghost:hover { border-color: var(--color-primary); color: var(--color-primary); }

.btn--onDark {
  background: color-mix(in srgb, var(--color-contrast-ink) 8%, transparent);
  border-color: color-mix(in srgb, var(--color-contrast-accent) 46%, transparent);
  color: var(--color-contrast-ink);
  -webkit-backdrop-filter: blur(8px);
  backdrop-filter: blur(8px);
}

.btn--onDark:hover {
  border-color: var(--color-contrast-accent);
  color: var(--color-contrast-accent);
  background: color-mix(in srgb, var(--color-contrast-accent) 12%, transparent);
}

/* ============================================================
   7. 标签、戳记、面包屑
   ============================================================ */
.tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 11px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: var(--color-ink-soft);
  border: var(--border-thin) solid color-mix(in srgb, var(--color-primary) 38%, var(--color-line));
  border-radius: var(--radius-pill);
  background: color-mix(in srgb, var(--color-surface) 62%, transparent);
}

.tag--accent {
  color: var(--color-accent);
  border-color: color-mix(in srgb, var(--color-accent) 48%, transparent);
  background: color-mix(in srgb, var(--color-highlight) 52%, transparent);
}

.badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 30px;
  padding: 3px 8px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  border-radius: var(--radius-sm);
  background: var(--color-primary);
  color: var(--color-primary-ink);
}

.badge--soft {
  background: color-mix(in srgb, var(--color-primary-soft) 76%, transparent);
  color: color-mix(in srgb, var(--color-primary) 78%, var(--color-contrast-surface));
}

.stamp {
  display: inline-flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-1) var(--space-2);
  padding: 6px 12px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.04em;
  color: var(--color-ink-muted);
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
  background: color-mix(in srgb, var(--color-surface) 68%, transparent);
}

.stamp__key { color: var(--color-ink-soft); letter-spacing: 0.1em; }
.stamp__value { color: var(--color-ink); font-variant-numeric: tabular-nums; }
.stamp__sep { color: var(--color-line); }

.section--contrast .stamp {
  color: color-mix(in srgb, var(--color-contrast-ink) 66%, transparent);
  border-color: var(--color-contrast-line);
  background: color-mix(in srgb, var(--color-contrast-ink) 5%, transparent);
}

.section--contrast .stamp__value { color: var(--color-contrast-ink); }

.breadcrumb {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-1) 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; gap: var(--space-2); }
.breadcrumb__item + .breadcrumb__item::before {
  content: "/";
  color: var(--color-line);
}
.breadcrumb a { transition: color 0.2s ease; }
.breadcrumb a:hover { color: var(--color-primary); }
.breadcrumb [aria-current="page"] { color: var(--color-ink); }

/* ============================================================
   8. 图片窗格与展签
   ============================================================ */
.media-frame {
  position: relative;
  overflow: hidden;
  border: var(--border-thin) solid color-mix(in srgb, var(--color-ink-soft) 24%, var(--color-line));
  border-radius: var(--radius-sm);
  background: var(--color-surface-deep);
  aspect-ratio: 16 / 10;
  isolation: isolate;
}

.media-frame--tall { aspect-ratio: 4 / 5; }
.media-frame--wide { aspect-ratio: 21 / 9; }
.media-frame--square { aspect-ratio: 1 / 1; }
.media-frame--plain { border-radius: 0; }

.media-frame > img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

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

.media-frame__caption {
  position: absolute;
  left: var(--space-2);
  bottom: var(--space-2);
  right: var(--space-2);
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  padding: 7px 12px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.05em;
  line-height: 1.5;
  color: var(--color-contrast-ink);
  background: color-mix(in srgb, var(--color-contrast-surface) 84%, transparent);
  border: var(--border-thin) solid color-mix(in srgb, var(--color-contrast-accent) 32%, transparent);
  border-radius: var(--radius-sm);
  -webkit-backdrop-filter: blur(9px);
  backdrop-filter: blur(9px);
}

.media-frame__caption-index { color: var(--color-contrast-accent); }
.media-frame__caption-more {
  display: none;
  color: color-mix(in srgb, var(--color-contrast-ink) 78%, transparent);
}

.media-frame:hover .media-frame__caption-more,
.media-frame:focus-within .media-frame__caption-more,
.media-frame[data-expanded="true"] .media-frame__caption-more {
  display: inline;
}

/* ============================================================
   9. 条目列表（可展开）
   ============================================================ */
.entry {
  border-bottom: var(--border-thin) solid var(--color-line);
}

.entry__head {
  display: flex;
  align-items: baseline;
  gap: var(--space-2) var(--space-3);
  width: 100%;
  padding: var(--space-3) var(--space-1);
  text-align: left;
  transition: background-color 0.2s ease;
}

.entry__head:hover { background: color-mix(in srgb, var(--color-primary-soft) 44%, transparent); }

.entry__num {
  flex: none;
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  letter-spacing: 0.06em;
  color: var(--color-accent);
  font-variant-numeric: tabular-nums;
}

.entry__title {
  flex: 1 1 auto;
  min-width: 0;
  font-family: var(--font-heading);
  font-size: var(--text-lg);
  font-weight: var(--weight-heading);
  line-height: 1.4;
}

.entry__meta {
  flex: none;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  color: var(--color-ink-muted);
  font-variant-numeric: tabular-nums;
}

.entry__body {
  display: none;
  padding: 0 var(--space-1) var(--space-4);
  max-width: var(--measure);
}

.entry[data-open="true"] .entry__body { display: block; }
.entry[data-open="true"] .entry__head { background: color-mix(in srgb, var(--color-primary-soft) 58%, transparent); }

.entry[data-open="true"] .entry__num { color: var(--color-primary); }

.aside-note {
  padding: var(--space-3);
  border: var(--border-thin) solid color-mix(in srgb, var(--color-primary) 28%, var(--color-line));
  border-radius: var(--radius-sm);
  background: color-mix(in srgb, var(--color-surface-alt) 66%, transparent);
  font-size: var(--text-sm);
  line-height: 1.7;
  color: var(--color-ink-soft);
}

.aside-note__title {
  display: block;
  margin-bottom: var(--space-2);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  color: var(--color-ink-muted);
}

/* ============================================================
   10. 页头
   ============================================================ */
.site-header {
  position: sticky;
  top: 0;
  z-index: 80;
  color: var(--color-contrast-ink);
  background: color-mix(in srgb, var(--color-contrast-surface) 66%, transparent);
  border-bottom: var(--border-thin) solid color-mix(in srgb, var(--color-contrast-accent) 20%, transparent);
  -webkit-backdrop-filter: blur(16px) saturate(140%);
  backdrop-filter: blur(16px) saturate(140%);
  transition: background-color 0.24s ease, box-shadow 0.24s ease, border-color 0.24s ease;
}

.site-header[data-scrolled="true"] {
  background: color-mix(in srgb, var(--color-contrast-surface) 94%, transparent);
  border-bottom-color: color-mix(in srgb, var(--color-contrast-ink) 20%, transparent);
  box-shadow: var(--shadow-2);
}

.site-header__inner {
  display: flex;
  align-items: center;
  gap: var(--space-2) var(--space-4);
  width: 100%;
  max-width: var(--container);
  min-height: 72px;
  margin-inline: auto;
  padding: 10px var(--gutter);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  min-width: 0;
  flex: 0 1 auto;
}

.brand__mark {
  flex: none;
  display: grid;
  place-items: center;
  width: 38px;
  height: 38px;
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  letter-spacing: 0.08em;
  color: var(--color-contrast-accent);
  border: var(--border-thin) solid color-mix(in srgb, var(--color-contrast-accent) 46%, transparent);
  border-radius: var(--radius-sm);
  background: color-mix(in srgb, var(--color-contrast-accent) 10%, transparent);
}

.brand__text { display: flex; flex-direction: column; min-width: 0; }

.brand__name {
  font-family: var(--font-heading);
  font-size: var(--text-lg);
  font-weight: var(--weight-heading);
  letter-spacing: 0.1em;
  line-height: 1.2;
  color: var(--color-contrast-ink);
}

.brand__line {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  color: color-mix(in srgb, var(--color-contrast-ink) 62%, transparent);
  white-space: nowrap;
}

.nav-toggle {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  margin-left: auto;
  padding: 9px 14px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.12em;
  color: var(--color-contrast-ink);
  border: var(--border-thin) solid color-mix(in srgb, var(--color-contrast-ink) 26%, transparent);
  border-radius: var(--radius-sm);
  background: color-mix(in srgb, var(--color-contrast-ink) 6%, transparent);
}

.nav-toggle__lines {
  display: inline-flex;
  flex-direction: column;
  gap: 4px;
  width: 16px;
}

.nav-toggle__lines > span {
  display: block;
  height: 1px;
  width: 100%;
  background: var(--color-contrast-accent);
  transition: transform 0.22s ease;
}

.nav-toggle[aria-expanded="true"] .nav-toggle__lines > span:first-child { transform: translateY(2.5px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] .nav-toggle__lines > span:last-child { transform: translateY(-2.5px) rotate(-45deg); }

.site-nav {
  display: none;
  position: absolute;
  left: 0;
  right: 0;
  top: 100%;
  max-height: min(74vh, 460px);
  overflow-y: auto;
  padding: var(--space-2) var(--gutter) var(--space-4);
  background: color-mix(in srgb, var(--color-contrast-surface) 97%, transparent);
  border-top: var(--border-thin) solid color-mix(in srgb, var(--color-contrast-ink) 16%, transparent);
  border-bottom: var(--border-thin) solid color-mix(in srgb, var(--color-contrast-ink) 16%, transparent);
  -webkit-backdrop-filter: blur(18px);
  backdrop-filter: blur(18px);
}

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

.site-nav__list {
  display: flex;
  flex-direction: column;
}

.site-nav__item { border-bottom: var(--border-thin) solid color-mix(in srgb, var(--color-contrast-ink) 12%, transparent); }

.site-nav__link {
  position: relative;
  display: flex;
  align-items: baseline;
  gap: var(--space-2);
  padding: 14px 2px;
  font-family: var(--font-heading);
  font-size: var(--text-base);
  letter-spacing: 0.06em;
  color: color-mix(in srgb, var(--color-contrast-ink) 86%, transparent);
  transition: color 0.2s ease;
}

.site-nav__index {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: color-mix(in srgb, var(--color-contrast-ink) 50%, transparent);
}

.site-nav__link::after {
  content: "";
  position: absolute;
  left: 2px;
  right: 2px;
  bottom: 6px;
  height: 1px;
  background: var(--color-contrast-accent);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 0.22s ease;
}

.site-nav__link:hover { color: var(--color-contrast-ink); }
.site-nav__link:hover::after { transform: scaleX(1); }

.site-nav__link[aria-current="page"] {
  color: var(--color-contrast-accent);
}

.site-nav__link[aria-current="page"] .site-nav__index { color: var(--color-contrast-accent); }
.site-nav__link[aria-current="page"]::after { transform: scaleX(1); }

.header-cta {
  display: none;
  flex: none;
  padding: 10px 20px;
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  font-weight: var(--weight-heading);
  letter-spacing: 0.08em;
  color: var(--color-contrast-ink);
  border: var(--border-thin) solid color-mix(in srgb, var(--color-contrast-accent) 46%, transparent);
  border-radius: var(--radius-pill);
  background: color-mix(in srgb, var(--color-contrast-accent) 10%, transparent);
  transition: border-color 0.2s ease, color 0.2s ease, background-color 0.2s ease;
}

.header-cta:hover {
  border-color: var(--color-contrast-accent);
  color: var(--color-contrast-accent);
  background: color-mix(in srgb, var(--color-contrast-accent) 18%, transparent);
}

.read-progress {
  position: absolute;
  left: 0;
  right: 0;
  bottom: -1px;
  height: 2px;
  background: color-mix(in srgb, var(--color-contrast-ink) 12%, transparent);
  pointer-events: none;
}

.read-progress__bar {
  display: block;
  width: 0;
  height: 100%;
  background: var(--color-contrast-accent);
}

@media (min-width: 640px) {
  .header-cta { display: inline-flex; }
}

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

  .site-nav,
  .site-nav[data-open="true"] {
    display: flex;
    position: static;
    margin-left: auto;
    max-height: none;
    overflow: visible;
    padding: 0;
    background: none;
    border: 0;
    -webkit-backdrop-filter: none;
    backdrop-filter: none;
  }

  .site-nav__list {
    flex-direction: row;
    flex-wrap: wrap;
    align-items: center;
    gap: var(--space-1) var(--space-3);
  }

  .site-nav__item { border-bottom: 0; }

  .site-nav__link {
    padding: 6px 1px;
    font-size: var(--text-sm);
  }

  .site-nav__link::after { bottom: 0; }

  .header-cta { margin-left: 0; }
}

/* ============================================================
   11. 页脚
   ============================================================ */
.site-footer {
  position: relative;
  margin-top: var(--section-y);
  padding: var(--space-6) 0 var(--space-4);
  color: var(--color-contrast-ink);
  background: var(--color-contrast-surface);
  isolation: isolate;
}

.site-footer::before {
  content: "";
  position: absolute;
  inset: 0;
  z-index: -1;
  background:
    radial-gradient(66% 70% at 8% 0%, color-mix(in srgb, var(--color-primary) 34%, transparent), transparent 62%),
    radial-gradient(52% 60% at 92% 26%, color-mix(in srgb, var(--color-accent) 26%, transparent), transparent 64%);
}

.site-footer__panel {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding: var(--space-4) var(--space-3);
  border: var(--border-thin) solid color-mix(in srgb, var(--color-contrast-ink) 18%, transparent);
  border-radius: var(--radius-lg);
  background: color-mix(in srgb, var(--color-contrast-ink) 5%, transparent);
  -webkit-backdrop-filter: blur(12px);
  backdrop-filter: blur(12px);
}

.site-footer__top {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: var(--space-6);
}

.site-footer__brand-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  margin-bottom: var(--space-3);
}

.site-footer__name {
  font-family: var(--font-heading);
  font-size: var(--text-xl);
  font-weight: var(--weight-heading);
  letter-spacing: 0.1em;
  margin: 0;
  color: var(--color-contrast-ink);
}

.site-footer__note {
  max-width: 42ch;
  margin: 0;
  font-size: var(--text-sm);
  line-height: 1.75;
  color: color-mix(in srgb, var(--color-contrast-ink) 68%, transparent);
}

.footer-index {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: var(--space-6) var(--space-4);
}

.footer-col__title {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin: 0 0 var(--space-3);
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  font-weight: var(--weight-heading);
  letter-spacing: 0.14em;
  color: var(--color-contrast-ink);
}

.footer-col__num {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: var(--color-contrast-accent);
}

.footer-col__title::after {
  content: "";
  flex: 1 1 auto;
  height: 1px;
  background: color-mix(in srgb, var(--color-contrast-ink) 20%, transparent);
}

.footer-col__list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.footer-col__link {
  position: relative;
  display: inline-block;
  font-size: var(--text-sm);
  line-height: 1.6;
  color: color-mix(in srgb, var(--color-contrast-ink) 80%, transparent);
  padding-bottom: 2px;
  transition: color 0.2s ease;
}

.footer-col__link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 1px;
  background: var(--color-contrast-accent);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 0.22s ease;
}

.footer-col__link:hover { color: var(--color-contrast-accent); }
.footer-col__link:hover::after { transform: scaleX(1); }

.footer-col__text {
  font-size: var(--text-sm);
  line-height: 1.72;
  color: color-mix(in srgb, var(--color-contrast-ink) 64%, transparent);
  max-width: 40ch;
}

.site-footer__legal {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  justify-content: space-between;
  gap: var(--space-2);
  margin-top: var(--space-6);
  padding-top: var(--space-3);
  border-top: var(--border-thin) solid var(--color-contrast-line);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.05em;
  color: color-mix(in srgb, var(--color-contrast-ink) 60%, transparent);
}

.site-footer__legal-line,
.site-footer__year { margin: 0; }

@media (min-width: 700px) {
  .site-footer__panel { padding: var(--space-6) var(--space-4); }
  .footer-index { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (min-width: 1000px) {
  .site-footer__panel { padding: var(--space-8) var(--space-6); }
  .site-footer__top { grid-template-columns: minmax(220px, 0.9fr) 2.6fr; }
  .footer-index { grid-template-columns: repeat(4, minmax(0, 1fr)); }
}

/* ============================================================
   12. 动效与降级
   ============================================================ */
[data-reveal] {
  opacity: 0;
  transform: translateY(12px);
  transition: opacity 0.26s ease, transform 0.26s ease;
}

[data-reveal][data-visible="true"] {
  opacity: 1;
  transform: none;
}

@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;
  }

  [data-reveal] {
    opacity: 1;
    transform: none;
  }

  [data-chapter] .section-label { opacity: 1; }
}

@media print {
  .site-header,
  .site-footer,
  .read-progress { display: none; }
}