/* ============================================================
   安博赛事 · 共享站点样式  /assets/site.css
   结构：reset → 变量 → 基础排版 → 布局工具 → 按钮链接
        → 头部 → 页脚 → 通用组件 → 响应式 → 焦点与动效偏好
   ============================================================ */

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

html { -webkit-text-size-adjust: 100%; text-size-adjust: 100%; scroll-padding-top: 132px; }

body,
h1, h2, h3, h4, h5, h6,
p, figure, blockquote, dl, dd, address { margin: 0; }

ul, ol { margin: 0; padding: 0; list-style: none; }

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

button, input, select, textarea { font: inherit; color: inherit; }

a { color: inherit; text-decoration: none; }

address { font-style: normal; }

/* ---------- 2. 变量 ---------- */
:root {
  --ab-void: #05070C;
  --ab-deep: #0B1220;
  --ab-raise: #121C2E;
  --ab-ink: #E9F3FF;
  --ab-body: #D2E1F3;
  --ab-muted: #8A9AB2;
  --ab-cyan: #00E5FF;
  --ab-orange: #FF7A1A;
  --ab-green: #3DFF9E;
  --ab-coral: #FF5468;
  --ab-line: #1F3A5F;
  --ab-glass: rgba(11, 18, 32, .72);

  --ab-maxw: 1440px;
  --ab-gutter: clamp(20px, 4.2vw, 88px);
  --ab-gap: clamp(16px, 1.6vw, 24px);
  --ab-radius: 14px;
  --ab-t: .18s;

  --ab-font-display: "Arial Narrow", "Helvetica Neue", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", system-ui, sans-serif;
  --ab-font-body: system-ui, -apple-system, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans SC", sans-serif;
  --ab-font-mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", "Courier New", monospace;
}

/* ---------- 3. 基础排版 ---------- */
html { scroll-behavior: smooth; }

body {
  min-height: 100vh;
  color: var(--ab-ink);
  font-family: var(--ab-font-body);
  font-size: 16px;
  line-height: 1.7;
  letter-spacing: .01em;
  overflow-x: hidden;
  background-color: var(--ab-void);
  background-image:
    radial-gradient(1000px 620px at 92% -12%, rgba(0, 229, 255, .10), transparent 60%),
    radial-gradient(820px 520px at -8% 4%, rgba(255, 122, 26, .08), transparent 58%),
    linear-gradient(180deg, #05070C 0%, #070B14 55%, #05070C 100%);
}

body.nav-open { overflow: hidden; }

h1, h2, h3, h4, h5, h6 {
  font-family: var(--ab-font-display);
  font-weight: 900;
  line-height: 1.12;
  letter-spacing: -.02em;
  font-stretch: 92%;
}

::selection { background: var(--ab-cyan); color: #04121A; }

.display-1 { font-size: clamp(44px, 7.4vw, 88px); line-height: .95; letter-spacing: -.03em; }
.section-title { font-size: clamp(24px, 3vw, 36px); }
.heading-3 { font-size: clamp(19px, 2vw, 24px); font-weight: 800; }

.eyebrow {
  font-family: var(--ab-font-mono);
  font-size: 12px;
  font-weight: 500;
  letter-spacing: .24em;
  text-transform: uppercase;
  color: var(--ab-cyan);
}

.lead { max-width: 56ch; font-size: clamp(17px, 1.5vw, 20px); line-height: 1.65; color: var(--ab-body); }

.mono, .timecode {
  font-family: var(--ab-font-mono);
  font-variant-numeric: tabular-nums;
  letter-spacing: .02em;
}
.timecode { color: var(--ab-cyan); }
.text-muted { color: var(--ab-muted); }

/* ---------- 4. 布局工具 ---------- */
.container {
  width: 100%;
  max-width: var(--ab-maxw);
  margin-inline: auto;
  padding-inline: var(--ab-gutter);
}

.section { position: relative; padding-block: clamp(52px, 7vw, 110px); }
.section--tight { padding-block: clamp(32px, 4vw, 64px); }

.grid12 {
  display: grid;
  grid-template-columns: repeat(12, minmax(0, 1fr));
  gap: var(--ab-gap);
}
.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-12 { grid-column: span 12; }

.split { display: grid; gap: clamp(24px, 3vw, 56px); align-items: start; }
.split--7-5 { grid-template-columns: minmax(0, 7fr) minmax(0, 5fr); }
.split--5-7 { grid-template-columns: minmax(0, 5fr) minmax(0, 7fr); }
.split--8-4 { grid-template-columns: minmax(0, 8fr) minmax(0, 4fr); }
.split--6-6 { grid-template-columns: minmax(0, 6fr) minmax(0, 6fr); }

.stack { display: grid; gap: var(--ab-gap); }
.stack--lg { gap: clamp(24px, 3vw, 44px); }

.section-head { display: grid; gap: 10px; max-width: 62ch; margin-bottom: clamp(24px, 3vw, 40px); }

.visually-hidden {
  position: absolute !important;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
  border: 0;
}

/* ---------- 5. 按钮与链接 ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: .5em;
  padding: .78em 1.3em;
  border: 1px solid transparent;
  border-radius: 8px;
  font-family: var(--ab-font-body);
  font-size: 15px;
  font-weight: 700;
  line-height: 1;
  letter-spacing: .02em;
  cursor: pointer;
  white-space: nowrap;
  transition: background var(--ab-t) ease, color var(--ab-t) ease,
              border-color var(--ab-t) ease, box-shadow var(--ab-t) ease,
              transform var(--ab-t) ease;
}
.btn:active { transform: translateY(1px); }

.btn--primary {
  background: var(--ab-orange);
  color: #05070C;
  box-shadow: 0 0 0 1px rgba(255, 122, 26, .45), 0 14px 34px -18px rgba(255, 122, 26, .95);
}
.btn--primary:hover { background: #FF8F3D; }

.btn--ghost {
  background: rgba(18, 28, 46, .55);
  border-color: var(--ab-line);
  color: var(--ab-ink);
}
.btn--ghost:hover { border-color: var(--ab-cyan); color: var(--ab-cyan); }

.btn--sm { padding: .6em 1.05em; font-size: 13px; }

.link-inline {
  color: var(--ab-cyan);
  border-bottom: 1px solid rgba(0, 229, 255, .35);
  transition: border-color var(--ab-t) ease;
}
.link-inline:hover { border-bottom-color: var(--ab-cyan); }

/* ---------- 6. 头部 ---------- */
.skip-link {
  position: fixed;
  top: 10px; left: 10px;
  z-index: 300;
  padding: .62em 1.05em;
  border-radius: 6px;
  background: var(--ab-cyan);
  color: #04121A;
  font-size: 14px;
  font-weight: 800;
  transform: translateY(-180%);
  transition: transform var(--ab-t) ease;
}
.skip-link:focus-visible { transform: translateY(0); outline: 2px solid #05070C; outline-offset: 2px; }

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  isolation: isolate;
  background: rgba(5, 7, 12, .86);
  border-bottom: 1px solid rgba(31, 58, 95, .95);
}
.site-header::before {
  content: "";
  position: absolute;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  -webkit-backdrop-filter: blur(14px) saturate(140%);
  backdrop-filter: blur(14px) saturate(140%);
}

/* 阅读进度轨 */
.scroll-progress {
  position: absolute;
  left: 0; right: 0; bottom: -1px;
  height: 2px;
  background: rgba(31, 58, 95, .55);
  pointer-events: none;
  z-index: 3;
}
.scroll-progress__bar {
  display: block;
  width: 0;
  height: 100%;
  background: linear-gradient(90deg, var(--ab-cyan), var(--ab-orange));
}

/* 状态播报条 */
.status-strip {
  position: relative;
  z-index: 1;
  overflow: hidden;
  height: 32px;
  display: flex;
  align-items: center;
  font-family: var(--ab-font-mono);
  font-size: 12px;
  letter-spacing: .06em;
  color: var(--ab-muted);
  background: linear-gradient(90deg, rgba(0, 229, 255, .14), rgba(255, 122, 26, .10));
  border-bottom: 1px solid rgba(31, 58, 95, .8);
}
.status-strip__track {
  display: flex;
  align-items: center;
  white-space: nowrap;
  padding-inline: var(--ab-gutter);
  animation: ab-slide 46s linear infinite;
}
.status-strip:hover .status-strip__track { animation-play-state: paused; }
.status-strip__item { display: inline-flex; align-items: center; padding-right: 2.75rem; }

@keyframes ab-slide {
  from { transform: translateX(0); }
  to { transform: translateX(-50%); }
}

.status-dot {
  width: 7px; height: 7px;
  margin-right: .6em;
  border-radius: 50%;
  display: inline-block;
  flex: none;
}
.status-dot--ok { background: var(--ab-green); box-shadow: 0 0 0 3px rgba(61, 255, 158, .14); animation: ab-pulse 2.4s ease-in-out infinite; }
.status-dot--warn { background: var(--ab-coral); box-shadow: 0 0 0 3px rgba(255, 84, 104, .14); }

@keyframes ab-pulse {
  0%, 100% { opacity: 1; box-shadow: 0 0 0 3px rgba(61, 255, 158, .14); }
  50% { opacity: .55; box-shadow: 0 0 0 6px rgba(61, 255, 158, .04); }
}

/* 品牌 + 导航 */
.header-bar { position: relative; z-index: 2; }

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: clamp(16px, 3vw, 48px);
  width: 100%;
  max-width: var(--ab-maxw);
  margin-inline: auto;
  padding: 14px var(--ab-gutter);
}

.brand { display: inline-flex; align-items: center; gap: 12px; flex: none; }

.brand__mark {
  position: relative;
  width: 28px; height: 28px;
  flex: none;
  background: linear-gradient(135deg, var(--ab-cyan), var(--ab-orange));
  clip-path: polygon(0 0, 100% 0, 100% 66%, 66% 100%, 0 100%);
}
.brand__mark::after {
  content: "";
  position: absolute;
  inset: 5px;
  background: var(--ab-void);
  clip-path: polygon(0 0, 100% 0, 100% 60%, 60% 100%, 0 100%);
}
.brand__mark--lg { width: 34px; height: 34px; }

.brand__name {
  display: block;
  font-family: var(--ab-font-display);
  font-weight: 900;
  font-stretch: 92%;
  font-size: 19px;
  letter-spacing: .02em;
  line-height: 1.15;
}
.brand__line {
  display: block;
  margin-top: 2px;
  font-family: var(--ab-font-mono);
  font-size: 11px;
  letter-spacing: .12em;
  color: var(--ab-muted);
}

.header-cluster {
  display: flex;
  align-items: center;
  gap: clamp(12px, 1.8vw, 28px);
}

.nav { display: flex; }
.nav__list { display: flex; align-items: center; gap: clamp(2px, .8vw, 14px); counter-reset: abnav; }
.nav__item { counter-increment: abnav; }

.nav__link {
  position: relative;
  display: inline-flex;
  align-items: baseline;
  gap: .5em;
  padding: 9px 10px;
  border-radius: 6px;
  font-size: 15px;
  color: var(--ab-muted);
  transition: color var(--ab-t) ease, background var(--ab-t) ease;
}
.nav__link::before {
  content: counter(abnav, decimal-leading-zero);
  font-family: var(--ab-font-mono);
  font-size: 10px;
  letter-spacing: .06em;
  color: var(--ab-line);
  transition: color var(--ab-t) ease;
}
.nav__link:hover { color: var(--ab-ink); background: rgba(0, 229, 255, .07); }
.nav__link:hover::before { color: var(--ab-cyan); }
.nav__link[aria-current="page"] { color: var(--ab-cyan); }
.nav__link[aria-current="page"]::before { color: var(--ab-cyan); }
.nav__link[aria-current="page"]::after {
  content: "";
  position: absolute;
  left: 10px; right: 10px; bottom: 2px;
  height: 2px;
  background: var(--ab-cyan);
  box-shadow: 0 0 12px rgba(0, 229, 255, .9);
}

.nav-toggle {
  display: none;
  align-items: center;
  gap: .6em;
  padding: .62em .9em;
  border: 1px solid var(--ab-line);
  border-radius: 8px;
  background: rgba(18, 28, 46, .6);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: .06em;
  cursor: pointer;
  transition: border-color var(--ab-t) ease, color var(--ab-t) ease;
}
.nav-toggle__bars { position: relative; display: block; width: 18px; height: 12px; }
.nav-toggle__bars::before,
.nav-toggle__bars::after {
  content: "";
  position: absolute;
  left: 0; right: 0;
  height: 2px;
  background: currentColor;
  transition: transform var(--ab-t) ease, top var(--ab-t) ease, bottom var(--ab-t) ease;
}
.nav-toggle__bars::before { top: 0; }
.nav-toggle__bars::after { bottom: 0; }

.site-header[data-open] .nav-toggle { border-color: var(--ab-cyan); color: var(--ab-cyan); }
.site-header[data-open] .nav-toggle__bars::before { top: 5px; transform: rotate(45deg); }
.site-header[data-open] .nav-toggle__bars::after { bottom: 5px; transform: rotate(-45deg); }

.header-angle {
  display: block;
  height: 2px;
  background: linear-gradient(90deg, var(--ab-cyan) 0%, rgba(0, 229, 255, .06) 46%, rgba(255, 122, 26, .85) 100%);
  clip-path: polygon(0 0, 78% 0, 68% 100%, 0 100%);
}

/* ---------- 7. 页脚 ---------- */
.site-footer {
  position: relative;
  margin-top: clamp(64px, 9vw, 140px);
  padding-block: clamp(44px, 5.5vw, 84px) 28px;
  border-top: 1px solid var(--ab-line);
  background: linear-gradient(180deg, #070B14 0%, #05070C 42%, #0B1220 100%);
}
.site-footer::before {
  content: "";
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--ab-orange), var(--ab-cyan));
  opacity: .85;
}

.footer-tier { padding-block: clamp(26px, 3.2vw, 44px); border-bottom: 1px solid rgba(31, 58, 95, .55); }
.footer-tier:last-of-type { border-bottom: 0; }

.tier-head { max-width: 62ch; margin-bottom: clamp(20px, 2.4vw, 32px); }
.tier-title { margin-top: 8px; font-size: clamp(22px, 2.6vw, 32px); }
.tier-note { margin-top: 8px; font-size: 15px; color: var(--ab-muted); }
.tier-foot {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 12px 18px;
  margin-top: clamp(20px, 2.4vw, 30px);
  font-size: 14px;
  color: var(--ab-muted);
}

.download-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: clamp(14px, 1.8vw, 26px);
}
.download-col {
  padding: 20px 18px 14px;
  border: 1px solid var(--ab-line);
  background: linear-gradient(160deg, var(--ab-raise), #0C1526);
}
.download-col__title {
  margin-bottom: 14px;
  padding-bottom: 10px;
  border-bottom: 1px dashed rgba(31, 58, 95, .95);
  font-family: var(--ab-font-mono);
  font-size: 13px;
  font-weight: 500;
  letter-spacing: .18em;
  text-transform: uppercase;
  color: var(--ab-cyan);
}
.download-list { display: grid; }
.download-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 10px 0;
  border-bottom: 1px solid rgba(31, 58, 95, .38);
  font-size: 14px;
}
.download-item:last-child { border-bottom: 0; }
.download-item__name { color: var(--ab-ink); }

.tag {
  flex: none;
  padding: 3px 9px;
  border: 1px solid var(--ab-line);
  border-radius: 999px;
  font-family: var(--ab-font-mono);
  font-size: 11px;
  letter-spacing: .08em;
  color: var(--ab-muted);
  white-space: nowrap;
}
.tag--fmt { color: var(--ab-cyan); border-color: rgba(0, 229, 255, .45); background: rgba(0, 229, 255, .08); }
.tag--ok { color: var(--ab-green); border-color: rgba(61, 255, 158, .4); background: rgba(61, 255, 158, .08); }
.tag--warn { color: var(--ab-coral); border-color: rgba(255, 84, 104, .4); background: rgba(255, 84, 104, .08); }

.footer-tier--feedback {
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(0, 1fr);
  gap: clamp(20px, 3vw, 44px);
  align-items: center;
  border-bottom: 1px solid rgba(31, 58, 95, .55);
}

.panel-glass {
  background: var(--ab-glass);
  border: 1px solid rgba(0, 229, 255, .22);
  border-radius: 16px;
  padding: clamp(20px, 2.4vw, 32px);
  -webkit-backdrop-filter: blur(12px);
  backdrop-filter: blur(12px);
  box-shadow: 0 30px 70px -48px rgba(0, 229, 255, .9);
}
.panel-solid {
  background: var(--ab-raise);
  border: 1px solid var(--ab-line);
  border-radius: var(--ab-radius);
  padding: clamp(18px, 2vw, 28px);
}
.cut-corner { clip-path: polygon(0 0, calc(100% - 18px) 0, 100% 18px, 100% 100%, 0 100%); }

.feedback-teaser__title { margin: 8px 0 10px; font-size: clamp(20px, 2.2vw, 27px); }
.feedback-teaser__text { max-width: 52ch; margin-bottom: 20px; font-size: 15px; color: var(--ab-body); }

.footer-status { display: grid; gap: 10px; }
.footer-status__row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 11px 14px;
  border-left: 2px solid var(--ab-line);
  background: rgba(11, 18, 32, .62);
  font-family: var(--ab-font-mono);
  font-size: 13px;
  letter-spacing: .04em;
  color: var(--ab-muted);
}
.footer-status__row--ok { border-left-color: var(--ab-green); }
.footer-status__row--warn { border-left-color: var(--ab-coral); }
.footer-status__row .mono { color: var(--ab-ink); }

.footer-tier--contact {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(0, 1.3fr) minmax(0, 1fr);
  gap: clamp(20px, 3vw, 44px);
}

.footer-brand__name {
  margin-top: 12px;
  font-family: var(--ab-font-display);
  font-weight: 900;
  font-stretch: 92%;
  font-size: 20px;
  letter-spacing: .02em;
}
.footer-brand__line { margin-top: 8px; max-width: 34ch; font-size: 14px; color: var(--ab-muted); }

.footer-contact { display: grid; gap: 12px; align-content: start; }
.footer-contact__row { display: grid; grid-template-columns: 88px minmax(0, 1fr); gap: 12px; font-size: 14px; }
.footer-contact__label {
  padding-top: 3px;
  font-family: var(--ab-font-mono);
  font-size: 11px;
  letter-spacing: .14em;
  text-transform: uppercase;
  color: var(--ab-muted);
}
.footer-contact__value { color: var(--ab-ink); word-break: break-word; }
.footer-contact__value.mono { color: var(--ab-cyan); }

.footer-legal__title {
  margin-bottom: 14px;
  font-family: var(--ab-font-mono);
  font-size: 11px;
  letter-spacing: .18em;
  text-transform: uppercase;
  color: var(--ab-muted);
}
.footer-legal__links { display: flex; flex-wrap: wrap; gap: 10px 20px; }
.footer-legal__links a {
  font-size: 14px;
  color: var(--ab-ink);
  border-bottom: 1px solid transparent;
  transition: color var(--ab-t) ease, border-color var(--ab-t) ease;
}
.footer-legal__links a:hover { color: var(--ab-cyan); border-bottom-color: var(--ab-cyan); }
.footer-legal__note { margin-top: 16px; font-size: 13px; line-height: 1.7; color: var(--ab-muted); }

.footer-bottom {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 10px 28px;
  margin-top: 10px;
  padding-top: 22px;
  border-top: 1px solid rgba(31, 58, 95, .55);
  font-family: var(--ab-font-mono);
  font-size: 12.5px;
  letter-spacing: .04em;
  color: var(--ab-muted);
}
.footer-bottom__icp { color: var(--ab-ink); }
.footer-bottom__note { max-width: 60ch; }

/* ---------- 8. 通用组件 ---------- */

/* 章节预览索引 */
.chapter-index { margin-top: clamp(22px, 2.6vw, 38px); }
.chapter-index__list {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 1px;
  background: var(--ab-line);
  border: 1px solid var(--ab-line);
}
.chapter-index__item { background: rgba(7, 11, 20, .92); }
.chapter-index__link { display: block; padding: 16px 18px; transition: background var(--ab-t) ease; }
.chapter-index__link:hover { background: rgba(0, 229, 255, .09); }
.chapter-index__num {
  display: block;
  font-family: var(--ab-font-mono);
  font-size: 12px;
  letter-spacing: .14em;
  color: var(--ab-cyan);
}
.chapter-index__label { display: block; margin-top: 6px; font-size: 16px; font-weight: 700; line-height: 1.4; }

/* 面包屑 */
.breadcrumb { padding-block: 14px; }
.breadcrumb__list {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  font-family: var(--ab-font-mono);
  font-size: 13px;
  color: var(--ab-muted);
}
.breadcrumb__item { display: flex; align-items: center; gap: 8px; }
.breadcrumb__item:not(:last-child)::after { content: "/"; color: var(--ab-line); }
.breadcrumb__link { transition: color var(--ab-t) ease; }
.breadcrumb__link:hover { color: var(--ab-cyan); }
.breadcrumb__current { color: var(--ab-ink); }

/* 正文容器 */
.prose { max-width: 68ch; font-size: 16.5px; line-height: 1.78; color: var(--ab-body); }
.prose > * + * { margin-top: 1.05em; }
.prose h2 { margin-top: 1.9em; font-size: 26px; font-weight: 900; color: var(--ab-ink); }
.prose h3 { margin-top: 1.6em; font-size: 20px; font-weight: 800; color: var(--ab-ink); }
.prose ul, .prose ol { display: grid; gap: .5em; }
.prose li { position: relative; padding-left: 1.4em; }
.prose li::before {
  content: "";
  position: absolute;
  left: 0; top: .66em;
  width: 8px; height: 2px;
  background: var(--ab-cyan);
}
.prose strong { color: var(--ab-ink); font-weight: 700; }
.prose a { color: var(--ab-cyan); border-bottom: 1px solid rgba(0, 229, 255, .35); }
.prose blockquote { padding-left: 18px; border-left: 2px solid var(--ab-orange); color: var(--ab-ink); }

/* 斜切分隔 */
.divider-angle {
  height: 1px;
  margin-block: clamp(28px, 4vw, 56px);
  background: linear-gradient(90deg, var(--ab-cyan), rgba(0, 229, 255, .05) 44%, rgba(255, 122, 26, .7));
}

/* 图片容器基础规则 */
.media-frame {
  position: relative;
  display: flex;
  align-items: flex-end;
  overflow: hidden;
  aspect-ratio: 16 / 9;
  border: 1px solid var(--ab-line);
  border-radius: var(--ab-radius);
  background:
    radial-gradient(120% 90% at 12% 0%, rgba(0, 229, 255, .18), transparent 55%),
    radial-gradient(90% 80% at 100% 100%, rgba(255, 122, 26, .16), transparent 60%),
    linear-gradient(150deg, #0B1220, #05070C);
}
.media-frame::before {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  opacity: .7;
  background-image: repeating-linear-gradient(115deg, rgba(31, 58, 95, .38) 0 1px, transparent 1px 68px);
}
.media-frame__media {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
}
.media-frame__caption {
  position: relative;
  z-index: 2;
  width: 100%;
  padding: 14px 18px;
  font-family: var(--ab-font-mono);
  font-size: 12px;
  letter-spacing: .06em;
  color: var(--ab-ink);
  background: linear-gradient(0deg, rgba(5, 7, 12, .92), rgba(5, 7, 12, 0));
}
.media-frame--wide { aspect-ratio: 21 / 9; }
.media-frame--4x3 { aspect-ratio: 4 / 3; }
.media-frame--tall { aspect-ratio: 3 / 4; }

/* 主题筛选 */
.filter-bar { display: flex; flex-wrap: wrap; align-items: center; gap: 10px; }
.filter-chip {
  padding: 8px 14px;
  border: 1px solid var(--ab-line);
  border-radius: 999px;
  background: rgba(11, 18, 32, .7);
  font-family: var(--ab-font-mono);
  font-size: 12px;
  letter-spacing: .1em;
  color: var(--ab-muted);
  cursor: pointer;
  transition: color var(--ab-t) ease, border-color var(--ab-t) ease, background var(--ab-t) ease;
}
.filter-chip:hover { border-color: var(--ab-cyan); color: var(--ab-ink); }
.filter-chip[aria-pressed="true"] {
  background: var(--ab-cyan);
  border-color: var(--ab-cyan);
  color: #04121A;
  font-weight: 700;
}
[data-filter-group] { transition: opacity .09s linear; }
[data-filter-group].is-swapping { opacity: 0; }
[data-filter-item][hidden] { display: none; }
.filter-status {
  font-family: var(--ab-font-mono);
  font-size: 12px;
  letter-spacing: .08em;
  color: var(--ab-muted);
}

/* 显现动效 */
.reveal { opacity: 0; transform: translateY(12px); transition: opacity .5s ease, transform .5s ease; }
.reveal.is-visible { opacity: 1; transform: none; }
.reveal--d1 { transition-delay: .06s; }
.reveal--d2 { transition-delay: .12s; }
.reveal--d3 { transition-delay: .18s; }

/* ---------- 9. 响应式 ---------- */
@media (max-width: 1180px) {
  .nav__link { font-size: 14px; padding: 9px 8px; }
  .header-cta { display: none; }
}

@media (max-width: 980px) {
  .split--7-5, .split--5-7, .split--8-4, .split--6-6 { grid-template-columns: minmax(0, 1fr); }
  .col-4, .col-5, .col-6, .col-7, .col-8 { grid-column: span 12; }
  .download-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .footer-tier--feedback { grid-template-columns: minmax(0, 1fr); }
  .footer-tier--contact { grid-template-columns: minmax(0, 1fr); }
}

@media (max-width: 900px) {
  .nav-toggle { display: inline-flex; }

  .nav {
    position: fixed;
    inset: 0;
    z-index: 1;
    display: block;
    padding: 112px var(--ab-gutter) 48px;
    overflow-y: auto;
    background: linear-gradient(160deg, #05070C 0%, #0B1220 58%, #101C33 100%);
    opacity: 0;
    visibility: hidden;
    transform: translateY(-8px);
    transition: opacity var(--ab-t) ease, transform var(--ab-t) ease, visibility var(--ab-t) ease;
  }
  .site-header[data-open] .nav { opacity: 1; visibility: visible; transform: none; }

  .nav__list { flex-direction: column; align-items: stretch; gap: 0; }
  .nav__item { border-bottom: 1px solid rgba(31, 58, 95, .7); }
  .nav__link {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 16px;
    padding: 20px 4px;
    border-radius: 0;
    font-family: var(--ab-font-display);
    font-weight: 900;
    font-stretch: 92%;
    font-size: clamp(22px, 6vw, 28px);
    letter-spacing: -.01em;
    color: var(--ab-ink);
    background: transparent;
  }
  .nav__link::before { order: 2; font-size: 12px; color: var(--ab-cyan); }
  .nav__link:hover { background: transparent; color: var(--ab-cyan); }
  .nav__link[aria-current="page"]::after {
    left: 4px; right: auto; bottom: 14px;
    width: 28px;
  }

  .header-inner { padding-block: 12px; }
  .brand__line { display: none; }
  .status-strip { height: 30px; font-size: 11px; }
  .status-strip__item { padding-right: 2rem; }
}

@media (max-width: 640px) {
  .download-grid { grid-template-columns: minmax(0, 1fr); }
  .footer-contact__row { grid-template-columns: minmax(0, 1fr); gap: 4px; }
  .footer-contact__label { padding-top: 0; }
  .footer-bottom { font-size: 12px; }
  .chapter-index__list { grid-template-columns: minmax(0, 1fr); }
}

/* ---------- 10. 焦点与动效偏好 ---------- */
:focus-visible {
  outline: 2px solid var(--ab-cyan);
  outline-offset: 3px;
  border-radius: 4px;
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: .001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: .001ms !important;
  }
  .status-strip { overflow-x: auto; }
  .status-strip__track { animation: none; }
  .scroll-progress__bar { transition: none; }
  .reveal { opacity: 1; transform: none; }
  [data-filter-group] { transition: none; }
  [data-filter-group].is-swapping { opacity: 1; }
}

@media (prefers-reduced-motion: no-preference) {
  html { scroll-behavior: smooth; }
}