:root {
  --color-surface: #ffffff;
  --color-surface-alt: #f5f5f5;
  --color-surface-deep: #e7e7e8;
  --color-ink: #3a343c;
  --color-ink-soft: #69606c;
  --color-ink-muted: #827986;
  --color-line: #dcdadc;
  --color-primary: #ab19e6;
  --color-primary-ink: #ffffff;
  --color-primary-soft: #f3dffc;
  --color-accent: #2c870d;
  --color-accent-ink: #ffffff;
  --color-highlight: #d9e9d3;
  --color-focus: #258505;
  --color-contrast-surface: #1d1022;
  --color-contrast-ink: #e6e4e7;
  --color-contrast-line: #493f4d;
  --color-contrast-accent: #4be916;
  --overlay-scrim: linear-gradient(180deg, rgba(29, 16, 34, 0.35) 0%, rgba(29, 16, 34, 0.72) 55%, rgba(29, 16, 34, 0.92) 100%);
  --font-heading: "Source Han Sans SC", "Noto Sans SC", SimHei, "Microsoft YaHei", sans-serif;
  --font-body: "PingFang SC", "Microsoft YaHei", "Source Han Sans SC", sans-serif;
  --font-mono: ui-monospace, Menlo, Consolas, monospace;
  --text-xs: 9.3px;
  --text-sm: 13.9px;
  --text-base: 17px;
  --text-lg: 25.5px;
  --text-xl: 38.2px;
  --text-2xl: 57.4px;
  --text-3xl: 86.1px;
  --text-4xl: 129.1px;
  --text-display: clamp(50px, 10.3vw, 132px);
  --text-figure: clamp(42px, 7.4vw, 95px);
  --weight-heading: 807;
  --weight-body: 400;
  --leading-body: 1.69;
  --leading-heading: 1.24;
  --tracking-heading: -0.019em;
  --radius-sm: 2px;
  --radius-md: 2px;
  --radius-lg: 2px;
  --radius-pill: 2px;
  --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: 74ch;
  --gutter: 32px;
  --section-y: 102px;
  --section-y-lg: 143px;
}

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

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

body {
  margin: 0;
  background: 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);
  word-break: break-word;
  overflow-wrap: anywhere;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4, h5, p, figure, blockquote, dl, dd, dt { margin: 0; }
ul, ol { margin: 0; padding: 0; list-style: none; }
img, svg, video { display: block; max-width: 100%; height: auto; }
button { font: inherit; color: inherit; background: none; border: 0; }
a { color: inherit; }
table { border-collapse: collapse; width: 100%; }
[id] { scroll-margin-top: 96px; }

h1, h2, h3, h4 {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  line-height: var(--leading-heading);
  letter-spacing: var(--tracking-heading);
  text-wrap: pretty;
}

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

/* ============ 布局工具 ============ */
.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--alt { background: var(--color-surface-alt); }
.section--deep { background: var(--color-surface-deep); }
.section--contrast {
  background: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}
.section--contrast .prose,
.section--contrast h1,
.section--contrast h2,
.section--contrast h3 { color: var(--color-contrast-ink); }
.section--contrast .prose a { color: var(--color-contrast-accent); }

.grid {
  display: grid;
  gap: var(--gutter);
}
.grid-7 { grid-template-columns: repeat(7, minmax(0, 1fr)); }
.col-span-2 { grid-column: span 2; }
.col-span-3 { grid-column: span 3; }
.col-span-4 { grid-column: span 4; }
.col-span-5 { grid-column: span 5; }
.col-span-7 { grid-column: span 7; }

.rule-dashed {
  height: 0;
  border: 0;
  border-top: var(--border-thin) dashed var(--color-line);
  margin: 0;
}
.section--contrast .rule-dashed { border-top-color: var(--color-contrast-line); }

/* ============ 区块起手式 ============ */
.section-head {
  display: grid;
  grid-template-columns: 4px minmax(0, 1fr);
  gap: var(--space-3);
  text-align: left;
  margin-bottom: var(--space-6);
  border-bottom: var(--border-thin) dashed var(--color-line);
  padding-bottom: var(--space-4);
}
.section--contrast .section-head { border-bottom-color: var(--color-contrast-line); }
.section-head::before {
  content: "";
  display: block;
  background: var(--color-primary);
  align-self: start;
  height: 100%;
  min-height: 44px;
}
.eyebrow {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.24em;
  text-transform: uppercase;
  color: var(--color-ink-muted);
  margin-bottom: var(--space-2);
}
.section--contrast .eyebrow { color: var(--color-contrast-accent); }
.section-title {
  font-size: var(--text-xl);
  color: var(--color-ink);
}
.section-lead {
  margin-top: var(--space-2);
  max-width: var(--measure);
  font-size: var(--text-base);
  color: var(--color-ink-soft);
}
.section--contrast .section-lead { color: var(--color-contrast-ink); }

/* ============ 跳至主要内容 ============ */
.skip-link {
  position: absolute;
  top: -120px;
  left: var(--space-2);
  z-index: 120;
  display: inline-block;
  padding: var(--space-2) var(--space-3);
  background: var(--color-primary);
  color: var(--color-primary-ink);
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  font-weight: 700;
  text-decoration: none;
  border-radius: var(--radius-sm);
  transition: top 0.18s ease;
}
.skip-link:focus { top: var(--space-2); }

/* ============ 头部框架条 ============ */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--color-surface);
  border-bottom: var(--border-thin) dashed var(--color-line);
}

.header-frame {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.header-bar {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
  align-items: center;
  gap: var(--space-4);
  min-height: 78px;
}

/* 品牌 */
.brand {
  display: flex;
  flex-direction: column;
  gap: 3px;
  padding-left: var(--space-2);
  border-left: 5px solid var(--color-primary);
  text-decoration: none;
  white-space: nowrap;
}
.brand-mark {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-lg);
  letter-spacing: var(--tracking-heading);
  line-height: 1.05;
  color: var(--color-ink);
}
.brand-sub {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  color: var(--color-ink-muted);
}
.brand:hover .brand-mark { color: var(--color-primary); }

/* 移动端开关 */
.nav-toggle {
  display: none;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-1) var(--space-2);
  border: var(--border-thin) dashed var(--color-line);
  border-radius: var(--radius-sm);
  background: var(--color-surface-alt);
  color: var(--color-ink);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.12em;
  cursor: pointer;
}
.nav-toggle-bars {
  display: block;
  width: 16px;
}
.nav-toggle-bar {
  display: block;
  height: 2px;
  margin-bottom: 3px;
  background: var(--color-primary);
}
.nav-toggle-bar:last-child { margin-bottom: 0; }
.nav-toggle[aria-expanded="true"] {
  border-style: solid;
  border-color: var(--color-primary);
  color: var(--color-primary);
}

/* 导航 */
.site-nav {
  display: flex;
  justify-content: center;
  min-width: 0;
}
.nav-list {
  display: flex;
  align-items: center;
  gap: 2px;
  min-width: 0;
}
.nav-link {
  display: block;
  padding: 10px var(--space-2);
  border-bottom: 3px solid transparent;
  border-radius: var(--radius-sm);
  color: var(--color-ink-soft);
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  font-weight: 700;
  text-decoration: none;
  white-space: nowrap;
  transition: color 0.16s ease, background-color 0.16s ease, border-color 0.16s ease;
}
.nav-link:hover {
  color: var(--color-ink);
  background: var(--color-surface-alt);
}
.nav-link[aria-current="page"] {
  color: var(--color-ink);
  border-bottom-color: var(--color-primary);
}
.nav-link[aria-current="page"]:hover { background: var(--color-primary-soft); }

/* V4 通道 */
.v4-channel {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: 11px var(--space-3);
  background: var(--color-primary);
  color: var(--color-primary-ink);
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  font-weight: 700;
  text-decoration: none;
  border-radius: var(--radius-sm);
  white-space: nowrap;
  transition: background-color 0.16s ease, transform 0.16s ease;
}
.v4-channel:hover {
  background: color-mix(in srgb, var(--color-primary) 82%, var(--color-contrast-surface));
  transform: translateY(-2px);
}
.v4-dot {
  display: block;
  width: 9px;
  height: 9px;
  background: var(--color-contrast-accent);
  border-radius: var(--radius-sm);
}
.v4-label { display: block; }

/* ============ 按钮 ============ */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: 12px var(--space-3);
  border: var(--border-thin) solid transparent;
  border-radius: var(--radius-sm);
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  font-weight: 700;
  text-decoration: none;
  cursor: pointer;
  transition: transform 0.16s ease, background-color 0.16s ease, color 0.16s ease, border-color 0.16s ease;
}
.btn:hover { transform: translateY(-2px); }
.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: transparent;
  color: var(--color-ink);
  border-color: var(--color-line);
}
.btn--ghost:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
}
.btn--contrast { background: var(--color-contrast-accent); color: var(--color-contrast-surface); }
.btn--contrast:hover { background: color-mix(in srgb, var(--color-contrast-accent) 78%, var(--color-surface)); }

/* ============ 标签 ============ */
.tag {
  display: inline-block;
  padding: 3px var(--space-1);
  border-radius: var(--radius-sm);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  line-height: 1.6;
}
.tag--primary { background: var(--color-primary-soft); color: color-mix(in srgb, var(--color-primary) 78%, var(--color-ink)); }
.tag--accent { background: var(--color-highlight); color: color-mix(in srgb, var(--color-accent) 82%, var(--color-ink)); }
.tag--contrast { background: var(--color-contrast-accent); color: var(--color-contrast-surface); }

/* ============ 正文排版 ============ */
.prose {
  max-width: var(--measure);
  font-size: var(--text-base);
  line-height: var(--leading-body);
  color: var(--color-ink);
}
.prose > * + * { margin-top: var(--space-3); }
.prose p { margin: 0; }
.prose h2 {
  font-size: var(--text-xl);
  margin-top: var(--space-6);
}
.prose h3 {
  font-size: var(--text-lg);
  margin-top: var(--space-4);
}
.prose ul, .prose ol {
  padding-left: var(--space-3);
  list-style: none;
}
.prose li { position: relative; padding-left: var(--space-3); margin-top: var(--space-2); }
.prose li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.72em;
  width: 10px;
  height: 2px;
  background: var(--color-primary);
}
.section--contrast .prose li::before { background: var(--color-contrast-accent); }
.prose a {
  color: var(--color-primary);
  text-decoration: underline;
  text-decoration-color: var(--color-primary-soft);
  text-decoration-thickness: 3px;
  text-underline-offset: 3px;
}
.prose a:hover { text-decoration-color: var(--color-primary); }
.prose strong { font-weight: 700; }
.prose blockquote {
  border-left: 5px solid var(--color-accent);
  padding-left: var(--space-3);
  color: var(--color-ink-soft);
}

.marker {
  background-image: linear-gradient(transparent 60%, var(--color-primary-soft) 60%);
  padding-inline: 0.08em;
}
.section--contrast .marker {
  background-image: linear-gradient(transparent 60%, color-mix(in srgb, var(--color-contrast-accent) 48%, transparent) 60%);
}
.hl {
  background: var(--color-highlight);
  color: color-mix(in srgb, var(--color-accent) 78%, var(--color-ink));
  padding-inline: 0.16em;
}
.num {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-feature-settings: "tnum" 1;
}

/* ============ 面包屑 ============ */
.breadcrumb {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  color: var(--color-ink-muted);
}
.breadcrumb ol {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-1);
}
.breadcrumb li { display: flex; align-items: center; gap: var(--space-1); }
.breadcrumb li + li::before {
  content: "/";
  color: var(--color-line);
}
.breadcrumb a { text-decoration: none; color: var(--color-ink-soft); }
.breadcrumb a:hover { color: var(--color-primary); }

/* ============ 图片容器 ============ */
.media-frame {
  position: relative;
  overflow: hidden;
  border-radius: var(--radius-sm);
  background: var(--color-surface-deep);
  margin: 0;
}
.media-frame img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}
.media-frame--16x9 { aspect-ratio: 16 / 9; }
.media-frame--4x5 { aspect-ratio: 4 / 5; }
.media-frame--1x1 { aspect-ratio: 1 / 1; }
.media-frame--scrim::after {
  content: "";
  position: absolute;
  inset: 0;
  background: var(--overlay-scrim);
  pointer-events: none;
}
.media-frame__body {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  z-index: 2;
  padding: var(--space-3);
  color: var(--color-contrast-ink);
}
.media-frame__body h3 { color: var(--color-contrast-ink); }

/* ============ 图例 / 坐标索引 ============ */
.legend {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: var(--color-ink-muted);
}
.legend-item { display: inline-flex; align-items: center; gap: var(--space-1); }
.legend-swatch {
  display: block;
  width: 12px;
  height: 12px;
  border-radius: var(--radius-sm);
  background: var(--color-primary);
}
.legend-swatch--accent { background: var(--color-accent); }
.legend-swatch--deep { background: var(--color-surface-deep); border: var(--border-thin) solid var(--color-line); }
.legend-swatch--contrast { background: var(--color-contrast-accent); }

/* ============ 主题筛选 ============ */
.filter-bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-2) 0;
  border-top: var(--border-thin) dashed var(--color-line);
  border-bottom: var(--border-thin) dashed var(--color-line);
}
.filter-btn {
  padding: 6px var(--space-2);
  border: var(--border-thin) dashed var(--color-line);
  border-radius: var(--radius-sm);
  background: transparent;
  color: var(--color-ink-soft);
  font-family: var(--font-heading);
  font-size: var(--text-sm);
  font-weight: 700;
  cursor: pointer;
  transition: background-color 0.16s ease, color 0.16s ease, border-color 0.16s ease;
}
.filter-btn:hover {
  color: var(--color-ink);
  border-color: var(--color-primary);
}
.filter-btn[aria-pressed="true"] {
  background: var(--color-primary);
  border-color: var(--color-primary);
  border-style: solid;
  color: var(--color-primary-ink);
}
.section--contrast .filter-bar { border-color: var(--color-contrast-line); }
.section--contrast .filter-btn {
  border-color: var(--color-contrast-line);
  color: var(--color-contrast-ink);
}
.section--contrast .filter-btn[aria-pressed="true"] {
  background: var(--color-contrast-accent);
  border-color: var(--color-contrast-accent);
  color: var(--color-contrast-surface);
}
[data-filter-item].is-filtered-out { display: none; }
.filter-empty {
  margin-top: var(--space-4);
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  color: var(--color-ink-muted);
}

/* ============ 滚动进度 ============ */
.scroll-progress {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  z-index: 70;
  background: transparent;
  pointer-events: none;
}
.scroll-progress__bar {
  display: block;
  width: 0;
  height: 100%;
  background: linear-gradient(90deg, var(--color-primary) 0%, var(--color-contrast-accent) 100%);
  transition: width 0.1s linear;
}

/* ============ 页脚 ============ */
.site-footer {
  background: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  margin-top: var(--section-y);
  padding-block: var(--space-8) var(--space-4);
  border-top: 5px solid var(--color-primary);
}
.site-footer :focus-visible { outline-color: var(--color-contrast-accent); }

.footer-frame {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.footer-grid {
  display: grid;
  grid-template-columns: 1.5fr 1fr 1.35fr 1fr;
  gap: var(--space-3);
  align-items: stretch;
}

.footer-panel {
  display: flex;
  flex-direction: column;
  padding: var(--space-4);
  background: color-mix(in srgb, var(--color-contrast-surface) 84%, var(--color-contrast-ink));
  border: var(--border-thin) solid var(--color-contrast-line);
  border-radius: var(--radius-sm);
}
.footer-panel--brand { border-top: 3px solid var(--color-primary); }
.footer-panel--contact { border-top: 3px solid var(--color-accent); }
.footer-panel--links { border-top: 3px solid var(--color-contrast-accent); }
.footer-panel--terms { border-top: 3px dashed var(--color-contrast-line); }

.footer-panel-title {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  font-weight: 400;
  letter-spacing: 0.26em;
  text-transform: uppercase;
  color: var(--color-contrast-accent);
  margin-bottom: var(--space-3);
}
.footer-panel--contact .footer-panel-title { color: var(--color-contrast-accent); }

.footer-brand {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-lg);
  line-height: 1.1;
  letter-spacing: var(--tracking-heading);
  color: var(--color-contrast-ink);
}
.footer-text {
  margin-top: var(--space-2);
  font-size: var(--text-sm);
  color: color-mix(in srgb, var(--color-contrast-ink) 78%, var(--color-contrast-surface));
}

.footer-meta {
  margin-top: var(--space-3);
  padding-top: var(--space-2);
  border-top: var(--border-thin) dashed var(--color-contrast-line);
  display: flex;
  flex-direction: column;
  gap: 6px;
}
.footer-meta-row {
  display: flex;
  align-items: baseline;
  gap: var(--space-2);
  font-size: var(--text-sm);
}
.footer-meta dt {
  flex: 0 0 3.2em;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.14em;
  color: color-mix(in srgb, var(--color-contrast-ink) 58%, var(--color-contrast-surface));
}
.footer-meta dd { color: var(--color-contrast-ink); }

.footer-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}
.footer-list--contact { gap: var(--space-2); }
.footer-list--contact li {
  display: flex;
  flex-direction: column;
  gap: 2px;
}
.footer-label {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.14em;
  color: color-mix(in srgb, var(--color-contrast-ink) 58%, var(--color-contrast-surface));
}
.footer-value {
  font-size: var(--text-sm);
  color: var(--color-contrast-ink);
}

.footer-link {
  display: inline-block;
  font-size: var(--text-sm);
  color: var(--color-contrast-ink);
  text-decoration: none;
  border-bottom: var(--border-thin) dashed transparent;
  padding-bottom: 1px;
  transition: color 0.16s ease, border-color 0.16s ease;
}
.footer-link:hover {
  color: var(--color-contrast-accent);
  border-bottom-color: var(--color-contrast-accent);
}

.footer-note {
  margin-top: var(--space-3);
  font-size: var(--text-xs);
  line-height: 1.7;
  color: color-mix(in srgb, var(--color-contrast-ink) 62%, var(--color-contrast-surface));
}

.footer-bottom {
  margin-top: var(--space-6);
  padding-top: var(--space-3);
  border-top: var(--border-thin) dashed var(--color-contrast-line);
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-3);
}
.footer-legal {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: color-mix(in srgb, var(--color-contrast-ink) 70%, var(--color-contrast-surface));
}
.footer-note--band {
  margin-top: 0;
  flex: 1 1 300px;
  min-width: 240px;
}

.to-top {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: 7px var(--space-2);
  border: var(--border-thin) solid var(--color-contrast-line);
  border-radius: var(--radius-sm);
  background: transparent;
  color: var(--color-contrast-accent);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.14em;
  cursor: pointer;
  transition: background-color 0.16s ease, color 0.16s ease, border-color 0.16s ease, transform 0.16s ease;
}
.to-top:hover {
  background: var(--color-contrast-accent);
  border-color: var(--color-contrast-accent);
  color: var(--color-contrast-surface);
  transform: translateY(-2px);
}

/* ============ 显现动画 ============ */
html[data-anim="on"] [data-reveal] {
  opacity: 0;
  transform: translateY(16px);
}
html[data-anim="on"] [data-reveal].is-revealed {
  opacity: 1;
  transform: none;
  transition: opacity 0.2s ease-out, transform 0.2s ease-out;
}

/* ============ 响应式 ============ */
@media (max-width: 1180px) {
  .nav-link { padding-inline: var(--space-1); }
  .footer-grid { grid-template-columns: 1.4fr 1fr 1.3fr; }
  .footer-panel--terms { grid-column: span 3; }
  .footer-panel--terms .footer-list { flex-direction: row; flex-wrap: wrap; gap: var(--space-3); }
}

@media (max-width: 1023px) {
  :root { --section-y: 72px; --section-y-lg: 96px; }

  .header-frame { padding-inline: var(--space-2); }
  .header-bar {
    grid-template-columns: auto auto minmax(0, 1fr);
    grid-template-areas:
      "brand toggle channel"
      "nav nav nav";
    gap: var(--space-2);
    padding-block: var(--space-2);
    min-height: 0;
  }
  .brand { grid-area: brand; border-left-width: 4px; padding-left: var(--space-1); }
  .brand-sub { display: none; }
  .brand-mark { font-size: var(--text-base); }
  .nav-toggle { grid-area: toggle; display: inline-flex; }
  .v4-channel { grid-area: channel; justify-self: end; padding: 9px var(--space-2); }
  .site-nav {
    grid-area: nav;
    display: none;
    justify-content: flex-start;
    width: 100%;
    padding-top: var(--space-2);
    border-top: var(--border-thin) dashed var(--color-line);
    overflow-x: auto;
    overscroll-behavior-x: contain;
    -webkit-overflow-scrolling: touch;
    scrollbar-width: thin;
  }
  .site-nav[data-open] { display: block; }
  .nav-list { gap: 0; }
  .nav-link { font-size: var(--text-sm); padding: 8px var(--space-2); }

  .grid-7 { grid-template-columns: repeat(2, minmax(0, 1fr)); gap: var(--space-4); }
  .col-span-3, .col-span-4, .col-span-5, .col-span-7 { grid-column: span 2; }
  .col-span-2 { grid-column: span 1; }

  .footer-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); gap: var(--space-2); }
  .footer-panel--terms { grid-column: span 2; }
  .footer-panel { padding: var(--space-3); }
  .footer-bottom { justify-content: flex-start; }
}

@media (max-width: 640px) {
  :root { --section-y: 56px; --section-y-lg: 72px; }

  .container { padding-inline: var(--space-2); }
  .header-frame, .footer-frame { padding-inline: var(--space-2); }
  .header-bar {
    grid-template-columns: minmax(0, 1fr) auto;
    grid-template-areas:
      "brand channel"
      "toggle toggle"
      "nav nav";
  }
  .nav-toggle { justify-self: start; width: 100%; justify-content: center; }
  .v4-channel { padding: 8px var(--space-2); font-size: var(--text-sm); }
  .v4-label { font-size: var(--text-sm); }

  .grid-7 { grid-template-columns: minmax(0, 1fr); }
  .col-span-2, .col-span-3, .col-span-4, .col-span-5, .col-span-7 { grid-column: span 1; }

  .footer-grid { grid-template-columns: minmax(0, 1fr); }
  .footer-panel--terms { grid-column: span 1; }
  .footer-panel--terms .footer-list { flex-direction: column; gap: var(--space-2); }

  .section-head { grid-template-columns: 3px minmax(0, 1fr); gap: var(--space-2); }
  .section-title { font-size: var(--text-lg); }
  .prose h2 { font-size: var(--text-lg); }
}

/* ============ 动效偏好 ============ */
@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;
  }
  html[data-anim="on"] [data-reveal],
  html[data-anim="on"] [data-reveal].is-revealed {
    opacity: 1;
    transform: none;
  }
  .btn:hover,
  .v4-channel:hover,
  .to-top:hover { transform: none; }
  .scroll-progress__bar { transition: none; }
}