/* =========================================================
   28圈平台主站 · 共享样式表 /assets/site.css
   蓝图网格 · 暖纸色与深墨色 · 等宽数字 · 极细边界
   ========================================================= */

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

html {
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: calc(76px + 20px);
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.85;
  color: var(--ink-950);
  background-color: var(--paper-100);
  background-image:
    linear-gradient(to right, rgba(174, 183, 192, 0.16) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(174, 183, 192, 0.12) 1px, transparent 1px);
  background-size: 96px 96px, 96px 96px;
  background-position: center top;
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4, h5, h6 { margin: 0; font-weight: 700; }
p { margin: 0; }
img, svg, video { display: block; max-width: 100%; }
button { font: inherit; color: inherit; background: none; border: 0; }
a { color: inherit; }
strong { font-weight: 700; }

/* ---------- 2. Tokens ---------- */
:root {
  --ink-950: #0A1520;
  --ink-800: #12283C;
  --ink-600: #24455F;
  --paper-100: #F6F2E9;
  --paper-200: #E9E3D6;
  --silver-400: #AEB7C0;
  --silver-200: #D7DCE1;
  --signal: #EB5A16;
  --signal-ink: #B23A0A;
  --cold-500: #3F6E9E;
  --hot-500: #A8455A;
  --focus: #2E8FB8;

  --font-head: 'Saira Condensed', 'Archivo Narrow', 'Noto Sans SC', 'PingFang SC', system-ui, sans-serif;
  --font-num: 'IBM Plex Mono', 'JetBrains Mono', ui-monospace, SFMono-Regular, Menlo, monospace;
  --font-body: 'Noto Sans SC', 'Source Han Sans SC', 'PingFang SC', 'Microsoft YaHei', system-ui, sans-serif;

  --header-h: 76px;
  --line: 1px solid var(--silver-200);
  --shadow-soft: 0 1px 0 rgba(10, 21, 32, 0.04), 0 18px 40px -34px rgba(10, 21, 32, 0.5);
  --shadow-lift: 0 24px 46px -30px rgba(10, 21, 32, 0.58);
}

/* ---------- 3. 通用工具 ---------- */
.sr-only {
  position: absolute;
  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;
}

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

.container {
  width: min(calc(100% - 40px), 1180px);
  margin-inline: auto;
}
.container--wide { width: min(calc(100% - 40px), 1360px); }
.container--narrow { width: min(calc(100% - 40px), 760px); }

.rule {
  height: 1px;
  margin: 0;
  border: 0;
  background: var(--silver-200);
}
.rule--tick {
  height: 11px;
  border-bottom: 1px solid var(--silver-200);
  background-color: transparent;
  background-image: repeating-linear-gradient(
    to right,
    var(--silver-200) 0 1px,
    transparent 1px 28px
  );
  background-repeat: repeat-x;
  background-position: left bottom;
  background-size: 100% 11px;
}

/* ---------- 4. 段落与栅格 ---------- */
.section {
  position: relative;
  padding-block: clamp(56px, 8vw, 104px);
}
.section--tight { padding-block: clamp(34px, 5vw, 64px); }
.section--lead { padding-top: calc(var(--header-h) + clamp(40px, 7vw, 92px)); }
.section--alt { background-color: var(--paper-200); }
.section--ink {
  background-color: var(--ink-950);
  color: rgba(246, 242, 233, 0.84);
}
.section--ink .section-head__title,
.section--ink .panel__title { color: var(--paper-100); }
.section--ink .section-head__lead,
.section--ink .prose { color: rgba(246, 242, 233, 0.7); }
.section--ink .stat__value { color: var(--paper-100); }
.section--ink .stat__label { color: var(--silver-400); }
.section--ink .stat { border-top-color: rgba(215, 220, 225, 0.22); }
.section--ink .rule,
.section--ink .rule--tick {
  background-color: rgba(215, 220, 225, 0.16);
  border-bottom-color: rgba(215, 220, 225, 0.16);
}

.grid {
  display: grid;
  gap: clamp(20px, 3vw, 44px);
}
.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--4-8 { grid-template-columns: 4fr 8fr; }
.grid--7-5 { grid-template-columns: 7fr 5fr; }
.grid--aside { grid-template-columns: minmax(170px, 3fr) 9fr; }

/* ---------- 5. 标题组与正文 ---------- */
.section-head {
  display: grid;
  gap: 12px;
  max-width: 68ch;
  margin-bottom: clamp(24px, 3.5vw, 46px);
}
.section-head__index {
  font-family: var(--font-num);
  font-size: 11.5px;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--signal-ink);
}
.section-head__title {
  font-family: var(--font-head);
  font-weight: 700;
  font-size: clamp(26px, 3.4vw, 44px);
  line-height: 1.1;
  letter-spacing: -0.01em;
  color: var(--ink-950);
}
.section-head__lead {
  max-width: 62ch;
  font-size: 16px;
  line-height: 1.85;
  color: var(--ink-600);
}

.prose {
  max-width: 68ch;
  font-size: 16px;
  line-height: 1.9;
  color: var(--ink-600);
}
.prose h2 {
  margin: 1.8em 0 0.6em;
  font-family: var(--font-head);
  font-size: 22px;
  line-height: 1.3;
  color: var(--ink-950);
}
.prose h3 {
  margin: 1.5em 0 0.5em;
  font-family: var(--font-head);
  font-size: 17px;
  line-height: 1.4;
  color: var(--ink-950);
}
.prose p { margin: 0 0 1.05em; }
.prose ul,
.prose ol { margin: 0 0 1.2em; padding-left: 1.3em; }
.prose li { margin-bottom: 0.4em; }
.prose a {
  color: var(--signal-ink);
  text-decoration: underline;
  text-underline-offset: 3px;
}
.prose strong { color: var(--ink-950); }

/* ---------- 6. 按钮 ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 22px;
  border: 1px solid transparent;
  border-radius: 0;
  font-family: var(--font-head);
  font-size: 14.5px;
  font-weight: 700;
  letter-spacing: 0.02em;
  line-height: 1.1;
  text-decoration: none;
  cursor: pointer;
  transition: background-color 0.2s ease, color 0.2s ease,
    border-color 0.2s ease, transform 0.2s ease, box-shadow 0.2s ease;
}
.btn--signal {
  background-color: var(--signal);
  border-color: var(--signal);
  color: #FFFFFF;
}
.btn--signal:hover {
  background-color: var(--signal-ink);
  border-color: var(--signal-ink);
  transform: translateY(-2px);
  box-shadow: 0 14px 26px -18px rgba(235, 90, 22, 0.9);
}
.btn--ghost {
  border-color: var(--silver-400);
  color: var(--ink-950);
}
.btn--ghost:hover {
  border-color: var(--ink-950);
  transform: translateY(-2px);
}
.section--ink .btn--ghost {
  border-color: rgba(215, 220, 225, 0.42);
  color: var(--paper-100);
}
.section--ink .btn--ghost:hover { border-color: var(--paper-100); }
.btn--sm { padding: 9px 15px; font-size: 13px; }
.btn--block { width: 100%; }

/* ---------- 7. 头部 ---------- */
.skip-link {
  position: fixed;
  left: 16px;
  top: -70px;
  z-index: 120;
  padding: 10px 16px;
  background-color: var(--ink-950);
  color: var(--paper-100);
  font-size: 14px;
  text-decoration: none;
  transition: top 0.18s ease;
}
.skip-link:focus { top: 12px; }

.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 80;
  color: var(--ink-950);
  background-color: transparent;
  transition: background-color 0.28s ease, color 0.28s ease, box-shadow 0.28s ease;
}
.site-header::before {
  content: "";
  position: absolute;
  inset: 0;
  background-image: linear-gradient(
    to bottom,
    rgba(246, 242, 233, 0.92),
    rgba(246, 242, 233, 0)
  );
  opacity: 1;
  transition: opacity 0.28s ease;
  pointer-events: none;
}
.site-header[data-scrolled="true"],
.site-header[data-nav-open="true"] {
  background-color: var(--ink-950);
  color: var(--paper-100);
  box-shadow: 0 1px 0 rgba(215, 220, 225, 0.16),
    0 18px 34px -26px rgba(10, 21, 32, 0.9);
}
.site-header[data-scrolled="true"]::before,
.site-header[data-nav-open="true"]::before { opacity: 0; }

.site-header__inner {
  position: relative;
  z-index: 1;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  min-height: var(--header-h);
}

.scroll-progress {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 2px;
  background-color: var(--signal);
  transform: scaleX(0);
  transform-origin: 0 50%;
  z-index: 2;
}

.site-header__brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: inherit;
}
.brand-mark {
  display: grid;
  place-items: center;
  width: 36px;
  height: 36px;
  border: 1px solid currentColor;
  box-shadow: inset 3px 0 0 0 var(--signal);
  font-family: var(--font-num);
  font-size: 14px;
  font-weight: 600;
  letter-spacing: 0.02em;
  opacity: 0.95;
}
.brand-text { display: flex; flex-direction: column; gap: 1px; }
.brand-name {
  font-family: var(--font-head);
  font-size: 18px;
  font-weight: 700;
  letter-spacing: 0.01em;
  line-height: 1.2;
}
.brand-tag {
  font-size: 11.5px;
  font-weight: 300;
  letter-spacing: 0.1em;
  opacity: 0.66;
  line-height: 1.4;
}

.site-nav {
  display: flex;
  align-items: center;
  gap: clamp(18px, 2.4vw, 34px);
}
.site-nav__list {
  display: flex;
  align-items: center;
  gap: clamp(12px, 1.7vw, 26px);
  margin: 0;
  padding: 0;
  list-style: none;
}
.site-nav__link {
  position: relative;
  display: inline-flex;
  align-items: baseline;
  gap: 6px;
  padding: 8px 2px;
  font-size: 14.5px;
  font-weight: 500;
  letter-spacing: 0.01em;
  text-decoration: none;
  color: inherit;
  opacity: 0.76;
  transition: opacity 0.2s ease, transform 0.2s ease, color 0.2s ease;
}
.site-nav__link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 2px;
  height: 1px;
  background-color: currentColor;
  transform: scaleX(0);
  transform-origin: 0 50%;
  transition: transform 0.22s ease, background-color 0.2s ease;
}
.site-nav__link:hover {
  opacity: 1;
  transform: translateY(-2px);
}
.site-nav__link:hover::after { transform: scaleX(1); }
.site-nav__link[aria-current="page"] {
  opacity: 1;
  color: var(--signal-ink);
}
.site-header[data-scrolled="true"] .site-nav__link[aria-current="page"],
.site-header[data-nav-open="true"] .site-nav__link[aria-current="page"] { color: var(--signal); }
.site-nav__link[aria-current="page"]::after {
  transform: scaleX(1);
  background-color: var(--signal);
}
.site-nav__index {
  font-family: var(--font-num);
  font-size: 10px;
  letter-spacing: 0.08em;
  opacity: 0.55;
}
.site-nav__actions { display: flex; align-items: center; }

.nav-toggle {
  display: none;
  align-items: center;
  justify-content: center;
  width: 46px;
  height: 46px;
  border: 1px solid currentColor;
  color: inherit;
  cursor: pointer;
  transition: background-color 0.2s ease;
}
.nav-toggle__bars {
  position: relative;
  display: block;
  width: 18px;
  height: 2px;
  background-color: currentColor;
  transition: background-color 0.2s ease;
}
.nav-toggle__bars::before,
.nav-toggle__bars::after {
  content: "";
  position: absolute;
  left: 0;
  width: 18px;
  height: 2px;
  background-color: currentColor;
  transition: transform 0.22s ease, top 0.22s ease;
}
.nav-toggle__bars::before { top: -6px; }
.nav-toggle__bars::after { top: 6px; }
.nav-toggle[aria-expanded="true"] .nav-toggle__bars { background-color: transparent; }
.nav-toggle[aria-expanded="true"] .nav-toggle__bars::before { top: 0; transform: rotate(45deg); }
.nav-toggle[aria-expanded="true"] .nav-toggle__bars::after { top: 0; transform: rotate(-45deg); }
.nav-toggle__text {
  position: absolute;
  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;
}

/* ---------- 8. 页脚 ---------- */
.site-footer {
  position: relative;
  padding-top: clamp(48px, 7vw, 86px);
  background-color: var(--ink-950);
  color: rgba(246, 242, 233, 0.84);
}
.site-footer::before {
  content: "";
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(to right, rgba(215, 220, 225, 0.07) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(215, 220, 225, 0.05) 1px, transparent 1px);
  background-size: 72px 72px, 72px 72px;
  pointer-events: none;
}
.site-footer > .container { position: relative; z-index: 1; }

.footer-grid {
  display: grid;
  grid-template-columns: 1.7fr repeat(3, 1fr);
  gap: clamp(26px, 3.4vw, 54px);
  padding-bottom: clamp(30px, 4vw, 54px);
  border-bottom: 1px solid rgba(215, 220, 225, 0.16);
}

.footer-brand { display: grid; gap: 10px; align-content: start; }
.footer-brand__mark {
  display: grid;
  place-items: center;
  width: 40px;
  height: 40px;
  border: 1px solid rgba(215, 220, 225, 0.42);
  box-shadow: inset 3px 0 0 0 var(--signal);
  font-family: var(--font-num);
  font-size: 15px;
  font-weight: 600;
  color: var(--paper-100);
}
.footer-brand__name {
  font-family: var(--font-head);
  font-size: 20px;
  font-weight: 700;
  letter-spacing: 0.01em;
  color: var(--paper-100);
}
.footer-brand__tag {
  font-size: 12px;
  font-weight: 300;
  letter-spacing: 0.12em;
  color: var(--silver-400);
}
.footer-brand__note {
  max-width: 34ch;
  margin-top: 4px;
  font-size: 13px;
  font-weight: 300;
  line-height: 1.8;
  color: rgba(246, 242, 233, 0.6);
}

.footer-col { display: grid; gap: 14px; align-content: start; }
.footer-col__title {
  padding-bottom: 10px;
  border-bottom: 1px solid rgba(215, 220, 225, 0.16);
  font-family: var(--font-num);
  font-size: 11.5px;
  font-weight: 500;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--silver-400);
}
.footer-col__list {
  display: grid;
  gap: 9px;
  margin: 0;
  padding: 0;
  list-style: none;
}
.footer-col__link {
  display: inline-block;
  font-size: 14.5px;
  color: rgba(246, 242, 233, 0.82);
  text-decoration: none;
  transition: color 0.2s ease, transform 0.2s ease;
}
.footer-col__link:hover {
  color: var(--signal);
  transform: translateY(-2px);
}

.footer-contact {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: clamp(16px, 2.4vw, 36px);
  padding: clamp(24px, 3vw, 38px) 0;
  border-bottom: 1px solid rgba(215, 220, 225, 0.16);
}
.footer-contact__item { display: grid; gap: 6px; }
.footer-contact__label {
  font-family: var(--font-num);
  font-size: 11px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--silver-400);
}
.footer-contact__value {
  font-size: 14px;
  color: rgba(246, 242, 233, 0.88);
  word-break: break-word;
}

.footer-bottom {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 14px 26px;
  padding: 22px 0 34px;
  font-size: 12.5px;
  font-weight: 300;
  color: rgba(246, 242, 233, 0.58);
}
.footer-bottom__legal { display: flex; flex-wrap: wrap; align-items: center; gap: 10px; }
.footer-legal__link {
  color: rgba(246, 242, 233, 0.78);
  text-decoration: none;
  border-bottom: 1px solid rgba(215, 220, 225, 0.3);
  transition: color 0.2s ease, border-color 0.2s ease;
}
.footer-legal__link:hover { color: var(--signal); border-color: var(--signal); }
.footer-legal__sep { color: rgba(215, 220, 225, 0.34); }
.footer-icp { font-family: var(--font-num); letter-spacing: 0.04em; }
.footer-meta { text-align: right; }

/* ---------- 9. 面包屑与目录 ---------- */
.breadcrumbs {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 9px;
  font-size: 12.5px;
  font-weight: 300;
  letter-spacing: 0.04em;
  color: var(--silver-400);
}
.breadcrumbs__link {
  color: var(--silver-400);
  text-decoration: none;
  transition: color 0.2s ease;
}
.breadcrumbs__link:hover { color: var(--signal-ink); }
.breadcrumbs__sep { font-family: var(--font-num); opacity: 0.7; }
.breadcrumbs__current { color: var(--ink-600); }

.toc {
  position: sticky;
  top: calc(var(--header-h) + 24px);
  display: grid;
  gap: 2px;
  align-content: start;
  font-size: 13.5px;
}
.toc__title {
  margin-bottom: 10px;
  font-family: var(--font-num);
  font-size: 11px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--silver-400);
}
.toc__link {
  display: block;
  padding: 8px 0 8px 12px;
  border-left: 1px solid var(--silver-200);
  color: var(--ink-600);
  text-decoration: none;
  line-height: 1.5;
  transition: color 0.2s ease, border-color 0.2s ease, padding-left 0.2s ease;
}
.toc__link:hover { color: var(--ink-950); border-color: var(--silver-400); }
.toc__link[aria-current="true"] {
  color: var(--signal-ink);
  border-color: var(--signal);
  padding-left: 16px;
}

/* ---------- 10. 数据组件 ---------- */
.panel {
  padding: clamp(18px, 2.4vw, 30px);
  border: 1px solid var(--silver-200);
  background-color: rgba(255, 255, 255, 0.55);
  box-shadow: var(--shadow-soft);
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}
.panel:hover {
  transform: translateY(-2px);
  border-color: var(--silver-400);
  box-shadow: var(--shadow-lift);
}
.panel--ink {
  background-color: var(--ink-800);
  border-color: rgba(215, 220, 225, 0.18);
  color: rgba(246, 242, 233, 0.84);
}
.panel--ink:hover { border-color: rgba(215, 220, 225, 0.36); }
.panel__title {
  margin-bottom: 8px;
  font-family: var(--font-head);
  font-size: 17px;
  font-weight: 700;
  line-height: 1.35;
  color: var(--ink-950);
}
.panel--ink .panel__title { color: var(--paper-100); }
.panel__meta {
  font-family: var(--font-num);
  font-size: 11.5px;
  letter-spacing: 0.08em;
  color: var(--silver-400);
}

.stat {
  display: grid;
  gap: 8px;
  padding: 18px 0;
  border-top: 1px solid var(--silver-200);
}
.stat__value {
  font-family: var(--font-num);
  font-size: clamp(34px, 5vw, 64px);
  font-weight: 600;
  line-height: 1;
  letter-spacing: -0.02em;
  color: var(--ink-950);
  font-variant-numeric: tabular-nums;
}
.stat__value--signal { color: var(--signal-ink); }
.stat__label {
  font-size: 13px;
  font-weight: 300;
  letter-spacing: 0.06em;
  color: var(--ink-600);
}

.tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 9px;
  border: 1px solid currentColor;
  font-family: var(--font-num);
  font-size: 11.5px;
  letter-spacing: 0.08em;
  line-height: 1.4;
  color: var(--ink-600);
}
.tag--cold { color: var(--cold-500); }
.tag--hot { color: var(--hot-500); }
.tag--signal { color: var(--signal-ink); }

.callout {
  padding: 16px 20px;
  border-left: 3px solid var(--signal);
  background-color: rgba(235, 90, 22, 0.07);
  font-size: 15px;
  line-height: 1.85;
  color: var(--ink-600);
}

.data-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14.5px;
}
.data-table th {
  padding: 10px 12px;
  border-bottom: 1px solid var(--silver-400);
  font-family: var(--font-head);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-align: left;
  color: var(--ink-600);
}
.data-table td {
  padding: 11px 12px;
  border-bottom: 1px solid var(--silver-200);
  font-variant-numeric: tabular-nums;
  color: var(--ink-600);
}
.data-table tbody tr:nth-child(even) { background-color: var(--paper-200); }
.data-table .num { color: var(--ink-950); }

/* ---------- 11. 图形容器 ---------- */
.figure { margin: 0; }
.figure__frame {
  position: relative;
  aspect-ratio: 16 / 9;
  overflow: hidden;
  border: 1px solid var(--silver-200);
  background-color: var(--paper-200);
  background-image:
    linear-gradient(to right, rgba(174, 183, 192, 0.22) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(174, 183, 192, 0.18) 1px, transparent 1px);
  background-size: 36px 36px, 36px 36px;
}
.figure__frame--wide { aspect-ratio: 21 / 9; }
.figure__frame--tall { aspect-ratio: 4 / 5; }
.figure__frame--square { aspect-ratio: 1 / 1; }
.figure__frame--ink {
  background-color: var(--ink-800);
  border-color: rgba(215, 220, 225, 0.18);
  background-image:
    linear-gradient(to right, rgba(215, 220, 225, 0.09) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(215, 220, 225, 0.07) 1px, transparent 1px);
}
.figure__img {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
}
.figure__caption {
  display: flex;
  gap: 10px;
  margin-top: 10px;
  font-size: 13px;
  font-weight: 300;
  line-height: 1.7;
  color: var(--ink-600);
}
.figure__caption::before {
  content: "";
  flex: 0 0 auto;
  width: 14px;
  height: 1px;
  margin-top: 9px;
  background-color: var(--signal);
}
.section--ink .figure__caption { color: rgba(246, 242, 233, 0.68); }

/* ---------- 12. 标签页与折叠 ---------- */
.tabs {
  display: flex;
  flex-wrap: wrap;
  border-bottom: 1px solid var(--silver-200);
}
.tab {
  padding: 11px 16px;
  border-bottom: 2px solid transparent;
  font-family: var(--font-head);
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 0.02em;
  color: var(--ink-600);
  cursor: pointer;
  transition: color 0.2s ease, border-color 0.2s ease, background-color 0.2s ease;
}
.tab:hover { color: var(--ink-950); background-color: rgba(233, 227, 214, 0.6); }
.tab[aria-selected="true"] {
  color: var(--ink-950);
  border-bottom-color: var(--signal);
}
.tabpanel { padding-top: 24px; animation: panel-in 0.12s ease-out both; }
.tabpanel[hidden] { display: none; }
@keyframes panel-in {
  from { opacity: 0; }
  to { opacity: 1; }
}

.fold { border-top: 1px solid var(--silver-200); }
.fold summary {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 16px;
  padding: 16px 0;
  font-family: var(--font-head);
  font-size: 17px;
  font-weight: 700;
  color: var(--ink-950);
  cursor: pointer;
  list-style: none;
}
.fold summary::-webkit-details-marker { display: none; }
.fold summary::after {
  content: "+";
  font-family: var(--font-num);
  font-size: 15px;
  color: var(--signal-ink);
}
.fold[open] summary::after { content: "–"; }
.fold__body {
  max-width: 66ch;
  padding: 0 0 18px;
  font-size: 15px;
  line-height: 1.85;
  color: var(--ink-600);
}

/* ---------- 13. 动效与返回顶部 ---------- */
.reveal { transition: opacity 0.5s ease, transform 0.5s ease; }
html.js-on .reveal { opacity: 0; transform: translateY(12px); }
html.js-on .reveal[data-visible="true"] { opacity: 1; transform: none; }

.to-top {
  position: fixed;
  right: 18px;
  bottom: 18px;
  z-index: 70;
  display: grid;
  place-items: center;
  width: 46px;
  height: 46px;
  border: 1px solid rgba(215, 220, 225, 0.32);
  background-color: var(--ink-950);
  color: var(--paper-100);
  font-family: var(--font-num);
  font-size: 13px;
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(8px);
  transition: opacity 0.22s ease, transform 0.22s ease, visibility 0.22s ease,
    background-color 0.2s ease, color 0.2s ease;
}
.to-top[data-visible="true"] {
  opacity: 1;
  visibility: visible;
  transform: none;
}
.to-top:hover {
  background-color: var(--signal);
  border-color: var(--signal);
  color: #FFFFFF;
}

/* ---------- 14. 焦点与降级 ---------- */
:focus-visible {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
}
.site-nav__link:focus-visible,
.footer-col__link:focus-visible,
.footer-legal__link:focus-visible,
.btn:focus-visible,
.tab:focus-visible,
.to-top:focus-visible,
.nav-toggle:focus-visible { outline: 2px solid var(--focus); outline-offset: 2px; }

/* ---------- 15. 响应式 ---------- */
@media (max-width: 1080px) {
  .footer-grid { grid-template-columns: 1.4fr repeat(3, 1fr); }
  .footer-contact { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (max-width: 900px) {
  :root { --header-h: 62px; }
  html { scroll-padding-top: calc(62px + 16px); }

  .brand-tag { display: none; }

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

  .site-nav {
    position: fixed;
    top: var(--header-h);
    left: 0;
    right: 0;
    z-index: 79;
    display: flex;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    max-height: calc(100vh - var(--header-h));
    padding: 6px 20px 26px;
    overflow-y: auto;
    border-top: 1px solid rgba(215, 220, 225, 0.16);
    background-color: var(--ink-950);
    color: var(--paper-100);
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
    transform: translateY(-8px);
    transition: opacity 0.2s ease, transform 0.22s ease, visibility 0.2s ease;
  }
  .site-nav[data-open="true"] {
    opacity: 1;
    visibility: visible;
    pointer-events: auto;
    transform: none;
  }
  .site-nav__list {
    flex-direction: column;
    align-items: stretch;
    gap: 0;
  }
  .site-nav__link {
    justify-content: flex-start;
    padding: 15px 2px;
    border-bottom: 1px solid rgba(215, 220, 225, 0.12);
    font-size: 17px;
    opacity: 0.9;
  }
  .site-nav__link:hover { transform: none; }
  .site-nav__link::after { bottom: 6px; }
  .site-nav__link[aria-current="page"] { color: var(--signal); }
  .site-nav__actions { margin-top: 20px; }
  .site-nav__actions .btn { width: 100%; padding: 14px 20px; font-size: 15px; }

  .footer-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .footer-brand { grid-column: 1 / -1; }
  .footer-meta { text-align: left; }
}

@media (max-width: 860px) {
  .grid--3,
  .grid--4,
  .grid--4-8,
  .grid--7-5,
  .grid--aside { grid-template-columns: minmax(0, 1fr); }
  .toc { position: static; }
}

@media (max-width: 620px) {
  .container,
  .container--wide,
  .container--narrow { width: calc(100% - 32px); }
  .grid--2 { grid-template-columns: minmax(0, 1fr); }
  .footer-grid { grid-template-columns: minmax(0, 1fr); }
  .footer-contact { grid-template-columns: minmax(0, 1fr); }
  .footer-bottom { flex-direction: column; align-items: flex-start; }
  .table-scroll { overflow-x: auto; }
}

/* ---------- 16. 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;
  }
  html.js-on .reveal { opacity: 1; transform: none; }
  .panel:hover,
  .btn:hover,
  .site-nav__link:hover,
  .footer-col__link:hover { transform: none; }
}