/* ==========================================================================
   win-kaixuan.com.cn — 共享样式 /assets/site.css
   夜航控制台：墨蓝底 · 左侧轨道导航 · 粗野主义描边与硬阴影
   ========================================================================== */

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

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

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

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

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

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

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

/* ---------- 2. tokens ---------- */
:root {
  /* 底色与分区 */
  --ink-900: #070C19;
  --ink-800: #0F1830;
  --ink-700: #1B2255;
  --wine-800: #5E1630;

  /* 语义强调 */
  --red: #E2233C;
  --red-bright: #FF5C6E;
  --cyan: #6FE3E1;
  --amber: #E7B23A;

  /* 文本与描边 */
  --silver: #9FB0C6;
  --paper: #EAF1FA;
  --graphite: #3A4A6B;

  /* 字号阶梯 */
  --fs-13: 13px;
  --fs-15: 15px;
  --fs-17: 17px;
  --fs-22: 22px;
  --fs-32: 32px;
  --fs-48: 48px;
  --fs-72: 72px;

  /* 间距体系 */
  --sp-8: 8px;
  --sp-16: 16px;
  --sp-24: 24px;
  --sp-40: 40px;
  --sp-64: 64px;

  /* 骨架尺寸 */
  --rail-w: 264px;
  --topbar-h: 62px;
  --line: 2px;

  --shadow-hard: 5px 5px 0 rgba(58, 74, 107, 0.85);
  --ease: 140ms ease;

  --font-sans: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei",
    "Source Han Sans SC", system-ui, -apple-system, "Segoe UI", sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Consolas,
    "Liberation Mono", "Courier New", monospace;
}

/* ---------- 3. 基础排版 ---------- */
body {
  background-color: var(--ink-900);
  background-image:
    radial-gradient(1200px 700px at 84% -14%, rgba(27, 34, 85, 0.72), transparent 72%),
    radial-gradient(900px 620px at -10% 108%, rgba(94, 22, 48, 0.5), transparent 72%);
  background-repeat: no-repeat;
  color: var(--paper);
  font-family: var(--font-sans);
  font-size: var(--fs-17);
  line-height: 1.8;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

h1, h2, h3, h4 {
  font-weight: 800;
  line-height: 1.22;
  letter-spacing: 0.08em;
}

h1 { font-size: var(--fs-48); }
h2 { font-size: var(--fs-32); }
h3 { font-size: var(--fs-22); }
h4 { font-size: var(--fs-17); }

::selection { background: var(--red); color: #fff; }

:focus-visible {
  outline: 2px solid var(--cyan);
  outline-offset: 2px;
  border-radius: 0;
}
:focus:not(:focus-visible) { outline: none; }

.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;
}

/* ---------- 4. 骨架：桌面端让出左侧轨道 ---------- */
@media (min-width: 1024px) {
  body { padding-left: var(--rail-w); }
}

/* ---------- 5. 页头 ---------- */
.site-header { position: relative; z-index: 60; }

.skip-link {
  position: fixed;
  top: 0; left: 0;
  z-index: 200;
  padding: 10px 18px;
  background: var(--cyan);
  color: #04121A;
  font-family: var(--font-mono);
  font-size: var(--fs-13);
  font-weight: 700;
  letter-spacing: 0.08em;
  border: var(--line) solid #04121A;
  transform: translateY(-140%);
  transition: transform 160ms ease;
}
.skip-link:focus { transform: translateY(0); }

.scroll-progress {
  position: fixed;
  top: 0; left: 0; right: 0;
  height: 2px;
  z-index: 90;
  background: var(--cyan);
  transform: scaleX(0);
  transform-origin: 0 50%;
  pointer-events: none;
  opacity: 0.9;
}

/* 顶部吸顶条：移动/平板可见 */
.topbar {
  position: sticky;
  top: 0;
  z-index: 60;
  display: flex;
  align-items: center;
  gap: var(--sp-16);
  min-height: var(--topbar-h);
  padding: 10px var(--sp-16);
  background: rgba(9, 14, 28, 0.94);
  border-bottom: var(--line) solid var(--graphite);
  backdrop-filter: blur(8px);
}
.topbar .brand { margin-right: auto; }

.topbar__stamp {
  display: none;
  padding: 3px 9px;
  border: 1px solid rgba(231, 178, 58, 0.45);
  color: var(--amber);
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.05em;
  white-space: nowrap;
}

/* 品牌 */
.brand {
  display: inline-flex;
  align-items: center;
  gap: var(--sp-16);
  min-width: 0;
  color: var(--paper);
}
.brand__mark {
  display: grid;
  place-items: center;
  flex: 0 0 auto;
  width: 44px;
  height: 44px;
  background: linear-gradient(140deg, var(--red), #8E1226);
  color: #FFF7F8;
  font-family: var(--font-mono);
  font-size: var(--fs-15);
  font-weight: 700;
  letter-spacing: 0.06em;
  clip-path: polygon(0 0, 100% 0, 100% calc(100% - 12px), calc(100% - 12px) 100%, 0 100%);
}
.brand__text {
  display: flex;
  flex-direction: column;
  min-width: 0;
  line-height: 1.28;
}
.brand__line {
  font-size: var(--fs-17);
  font-weight: 700;
  letter-spacing: 0.1em;
}
.brand__note {
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--silver);
  letter-spacing: 0.04em;
}

/* 汉堡按钮 */
.nav-toggle {
  display: inline-flex;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  flex: 0 0 auto;
  width: 46px;
  height: 44px;
  padding: 0 11px;
  background: var(--ink-800);
  border: var(--line) solid var(--graphite);
  color: var(--paper);
  cursor: pointer;
  transition: border-color var(--ease), background var(--ease);
}
.nav-toggle:hover { border-color: var(--cyan); background: var(--ink-700); }
.nav-toggle__bar {
  display: block;
  width: 100%;
  height: 2px;
  background: var(--cyan);
  transition: transform var(--ease), opacity var(--ease);
}
.nav-toggle[aria-expanded="true"] .nav-toggle__bar:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] .nav-toggle__bar:nth-child(2) { opacity: 0; }
.nav-toggle[aria-expanded="true"] .nav-toggle__bar:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* 侧边轨道 / 移动抽屉 */
.rail {
  position: fixed;
  top: 0; right: 0;
  z-index: 70;
  width: min(86vw, 340px);
  height: 100vh;
  height: 100dvh;
  display: flex;
  flex-direction: column;
  gap: var(--sp-24);
  padding: var(--sp-24) var(--sp-24) var(--sp-40);
  overflow-y: auto;
  background-color: var(--ink-800);
  background-image:
    repeating-linear-gradient(180deg, rgba(159, 176, 198, 0.05) 0 1px, transparent 1px 5px),
    linear-gradient(180deg, var(--ink-800), var(--ink-900) 62%);
  border-left: var(--line) solid var(--graphite);
  transform: translateX(102%);
  transition: transform 220ms ease;
}
.rail[data-open="true"] { transform: translateX(0); }

.rail-scrim {
  position: fixed;
  inset: 0;
  z-index: 65;
  background: rgba(7, 12, 25, 0.74);
  backdrop-filter: blur(2px);
  opacity: 0;
  pointer-events: none;
  transition: opacity 200ms ease;
}
.rail[data-open="true"] + .rail-scrim {
  opacity: 1;
  pointer-events: auto;
}

html[data-nav-open="true"] { overflow: hidden; }

.rail__head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--sp-16);
  padding-bottom: var(--sp-16);
  border-bottom: var(--line) solid var(--graphite);
}
.rail__close {
  display: inline-flex;
  align-items: center;
  gap: var(--sp-8);
  padding: 8px 12px;
  background: transparent;
  border: var(--line) solid var(--graphite);
  color: var(--silver);
  font-size: var(--fs-13);
  letter-spacing: 0.08em;
  cursor: pointer;
  transition: border-color var(--ease), color var(--ease);
}
.rail__close:hover { border-color: var(--cyan); color: var(--cyan); }
.rail__close-text { font-family: var(--font-mono); }

.rail__nav { flex: 1 0 auto; }
.rail__nav-title {
  margin-bottom: 10px;
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--silver);
}

.nav-list { display: flex; flex-direction: column; gap: 2px; }
.nav-item { position: relative; }

.nav-link {
  display: flex;
  align-items: baseline;
  gap: 12px;
  padding: 10px 12px 10px 14px;
  color: var(--silver);
  font-size: var(--fs-15);
  letter-spacing: 0.04em;
  border-left: 3px solid transparent;
  transition: background var(--ease), color var(--ease), border-color var(--ease);
}
.nav-link:hover {
  background: rgba(111, 227, 225, 0.08);
  color: var(--paper);
  border-left-color: var(--cyan);
}
.nav-link[aria-current="page"] {
  color: var(--paper);
  border-left-color: var(--red);
  background: linear-gradient(90deg, rgba(226, 35, 60, 0.22), transparent 88%);
}
.nav-link__idx {
  flex: 0 0 auto;
  font-family: var(--font-mono);
  font-size: var(--fs-13);
  letter-spacing: 0.05em;
  color: var(--amber);
}
.nav-link[aria-current="page"] .nav-link__idx { color: var(--red-bright); }
.nav-link__label { min-width: 0; }

.rail__foot {
  margin-top: auto;
  display: flex;
  flex-direction: column;
  gap: var(--sp-16);
  padding-top: var(--sp-24);
  border-top: var(--line) solid var(--graphite);
}
.readout { display: grid; gap: var(--sp-8); }
.readout__row {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
}
.readout__label {
  font-size: var(--fs-13);
  letter-spacing: 0.05em;
  color: var(--silver);
}
.readout__value {
  font-family: var(--font-mono);
  font-size: 15px;
  font-weight: 600;
  color: var(--paper);
  letter-spacing: 0.03em;
}
.readout__value--date { color: var(--amber); }
.rail__actions { display: grid; gap: var(--sp-8); }

/* 桌面端：轨道固定左侧 */
@media (min-width: 1024px) {
  .topbar { display: none; }
  .rail-scrim { display: none; }
  .scroll-progress { left: var(--rail-w); }
  .rail {
    left: 0;
    right: auto;
    width: var(--rail-w);
    padding: 32px var(--sp-24) var(--sp-24);
    border-left: 0;
    border-right: var(--line) solid var(--graphite);
    transform: none;
    transition: none;
  }
  .rail__close { display: none; }
}
@media (min-width: 480px) {
  .topbar__stamp { display: inline-block; }
}

/* ---------- 6. 按钮 ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-8);
  padding: 11px 18px;
  background: var(--ink-800);
  border: var(--line) solid var(--graphite);
  color: var(--paper);
  font-size: var(--fs-15);
  letter-spacing: 0.06em;
  text-align: center;
  cursor: pointer;
  transition: background var(--ease), color var(--ease),
    border-color var(--ease), transform var(--ease), box-shadow var(--ease);
}
.btn:hover {
  border-color: var(--cyan);
  color: var(--cyan);
  transform: translateY(-2px);
  box-shadow: var(--shadow-hard);
}
.btn--primary {
  background: var(--red);
  border-color: var(--red);
  color: #FFF5F6;
  font-weight: 700;
  letter-spacing: 0.08em;
}
.btn--primary:hover {
  background: var(--red-bright);
  border-color: var(--red-bright);
  color: #25060C;
}
.btn--ghost {
  background: transparent;
  color: var(--silver);
}
.btn--ghost:hover { color: var(--cyan); }
.btn--block { width: 100%; }

/* ---------- 7. 布局与分区 ---------- */
.container {
  width: 100%;
  max-width: 1200px;
  margin-inline: auto;
  padding-inline: var(--sp-24);
}
.container--wide { max-width: 1440px; }

.section { position: relative; padding-block: var(--sp-64); }
.section--tight { padding-block: var(--sp-40); }
.section--indigo { background: linear-gradient(180deg, var(--ink-700), #131A42); }
.section--wine { background: linear-gradient(180deg, var(--wine-800), #3E0F20); }

.has-scan { position: relative; }
.has-scan::after {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  background-image: repeating-linear-gradient(
    180deg,
    rgba(159, 176, 198, 0.06) 0 1px,
    transparent 1px 4px
  );
  animation: scan-drift 18s linear infinite;
}
@keyframes scan-drift {
  from { background-position-y: 0; }
  to { background-position-y: 48px; }
}

.grid { display: grid; gap: var(--sp-24); }
.grid--2 { grid-template-columns: 1fr; }
.grid--3 { grid-template-columns: 1fr; }
@media (min-width: 768px) {
  .grid--2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .grid--3 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}
@media (min-width: 1280px) {
  .grid--3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
}

.divider {
  height: var(--line);
  border: 0;
  margin-block: var(--sp-40);
  background: linear-gradient(90deg, var(--graphite), rgba(58, 74, 107, 0) 78%);
}

/* ---------- 8. 卡片面板 ---------- */
.panel {
  position: relative;
  display: flex;
  flex-direction: column;
  padding: var(--sp-24);
  background: var(--ink-800);
  border: var(--line) solid var(--graphite);
  clip-path: polygon(0 0, calc(100% - 18px) 0, 100% 18px, 100% 100%, 18px 100%, 0 calc(100% - 18px));
  filter: drop-shadow(5px 5px 0 rgba(58, 74, 107, 0.72));
  transition: transform var(--ease), border-color var(--ease), filter var(--ease);
}
.panel:hover {
  transform: translateY(-2px);
  border-color: var(--cyan);
  filter: drop-shadow(7px 7px 0 rgba(111, 227, 225, 0.35));
}
.panel--indigo { background: linear-gradient(160deg, var(--ink-700), #131A42); }
.panel--wine { background: linear-gradient(160deg, var(--wine-800), #3E0F20); }

.panel__title {
  margin-bottom: 12px;
  font-size: var(--fs-22);
  font-weight: 800;
  letter-spacing: 0.08em;
}
.panel__meta {
  font-family: var(--font-mono);
  font-size: var(--fs-13);
  letter-spacing: 0.05em;
  color: var(--silver);
}
.panel__foot {
  margin-top: auto;
  padding-top: var(--sp-16);
  border-top: 1px dashed rgba(58, 74, 107, 0.85);
}

/* ---------- 9. 状态条 / 标签 / 索引 ---------- */
.status-strip {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: var(--line);
  background: var(--graphite);
  border: var(--line) solid var(--graphite);
}
.status-strip__cell {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 12px 16px;
  background: var(--ink-800);
}

.tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 3px 9px;
  border: 1px solid var(--graphite);
  color: var(--silver);
  font-family: var(--font-mono);
  font-size: var(--fs-13);
  letter-spacing: 0.05em;
}
.tag--cyan { color: var(--cyan); border-color: rgba(111, 227, 225, 0.55); }
.tag--red { color: var(--red-bright); border-color: rgba(226, 35, 60, 0.62); }
.tag--amber { color: var(--amber); border-color: rgba(231, 178, 58, 0.55); }

.label {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--silver);
}

.num {
  font-family: var(--font-mono);
  font-weight: 600;
  font-size: 1.1em;
  letter-spacing: 0.04em;
  color: var(--amber);
}

.index-list { display: flex; flex-direction: column; }
.index-item {
  display: flex;
  align-items: baseline;
  gap: 12px;
  padding: 10px 0;
  border-bottom: 1px dashed rgba(58, 74, 107, 0.7);
}
.index-item:last-child { border-bottom: 0; }
.index-item__num {
  flex: 0 0 auto;
  min-width: 2.6em;
  font-family: var(--font-mono);
  font-size: var(--fs-13);
  color: var(--amber);
  letter-spacing: 0.05em;
}
.index-item__text { min-width: 0; color: var(--silver); }
.index-item__text a {
  color: var(--paper);
  border-bottom: 1px solid var(--graphite);
  transition: color var(--ease), border-color var(--ease);
}
.index-item__text a:hover { color: var(--cyan); border-bottom-color: var(--cyan); }

.index-strip {
  display: flex;
  gap: var(--sp-8);
  overflow-x: auto;
  padding-bottom: 6px;
  scrollbar-width: thin;
}
.index-strip__item {
  flex: 0 0 auto;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 8px 14px;
  background: var(--ink-800);
  border: var(--line) solid var(--graphite);
  color: var(--silver);
  font-size: var(--fs-13);
  letter-spacing: 0.05em;
  transition: border-color var(--ease), color var(--ease), background var(--ease);
}
.index-strip__item:hover {
  border-color: var(--cyan);
  color: var(--cyan);
  background: var(--ink-700);
}

/* ---------- 10. 长文与面包屑 ---------- */
.prose {
  max-width: 38em;
  color: var(--paper);
  font-size: var(--fs-17);
  line-height: 1.8;
}
.prose p { margin-bottom: 1.1em; }
.prose h2 { margin: 1.6em 0 0.6em; font-size: var(--fs-32); }
.prose h3 { margin: 1.4em 0 0.5em; font-size: var(--fs-22); }
.prose ul,
.prose ol { margin-bottom: 1.2em; padding-left: 1.5em; }
.prose ul li { list-style: square; }
.prose ol li { list-style: decimal; }
.prose li { margin: 0.35em 0; }
.prose strong { color: #FFFFFF; }
.prose a { color: var(--cyan); text-decoration: underline; text-underline-offset: 3px; }
.prose code {
  padding: 1px 6px;
  background: var(--ink-800);
  border: 1px solid var(--graphite);
  font-family: var(--font-mono);
  font-size: 0.92em;
}

.breadcrumbs {
  font-size: var(--fs-13);
  letter-spacing: 0.05em;
  color: var(--silver);
}
.breadcrumbs ol { display: flex; flex-wrap: wrap; gap: 8px; }
.breadcrumbs li::after { content: "/"; margin-left: 8px; color: var(--graphite); }
.breadcrumbs li:last-child::after { content: none; }
.breadcrumbs a { border-bottom: 1px solid transparent; transition: color var(--ease), border-color var(--ease); }
.breadcrumbs a:hover { color: var(--cyan); border-bottom-color: var(--cyan); }

/* ---------- 11. 图片容器 ---------- */
.media {
  position: relative;
  display: block;
  overflow: hidden;
  aspect-ratio: 3 / 2;
  background: var(--ink-700);
  border: var(--line) solid var(--graphite);
}
.media img { width: 100%; height: 100%; object-fit: cover; }
.media--4x3 { aspect-ratio: 4 / 3; }
.media--ui { box-shadow: inset 0 0 0 1px rgba(111, 227, 225, 0.45); }
.media--empty {
  background-image: repeating-linear-gradient(
    45deg,
    rgba(58, 74, 107, 0.55) 0 8px,
    rgba(15, 24, 48, 0.92) 8px 16px
  );
}
.media__tag {
  position: absolute;
  top: 10px; left: 10px;
  padding: 2px 8px;
  background: rgba(7, 12, 25, 0.86);
  border: 1px solid rgba(231, 178, 58, 0.55);
  color: var(--amber);
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.05em;
}
.media__caption {
  position: absolute;
  left: 0; right: 0; bottom: 0;
  padding: 10px 12px;
  background: linear-gradient(180deg, transparent, rgba(7, 12, 25, 0.94));
  color: var(--silver);
  font-family: var(--font-mono);
  font-size: var(--fs-13);
  letter-spacing: 0.04em;
}

/* ---------- 12. 页脚 ---------- */
.site-footer {
  position: relative;
  margin-top: var(--sp-64);
  padding: var(--sp-64) 0 var(--sp-24);
  background: var(--ink-800);
  border-top: 4px solid var(--red);
}

.footer__grid {
  display: grid;
  gap: var(--sp-40);
  grid-template-columns: 1fr;
}
@media (min-width: 768px) {
  .footer__grid { grid-template-columns: 1fr 1.6fr; }
}
@media (min-width: 1024px) {
  .footer__grid { grid-template-columns: 1fr 1.8fr 1.1fr; }
}

.footer__brand-line {
  font-size: var(--fs-22);
  font-weight: 800;
  letter-spacing: 0.14em;
}
.footer__slogan {
  margin-top: 6px;
  color: var(--cyan);
  font-size: var(--fs-17);
  letter-spacing: 0.06em;
}
.footer__note {
  margin-top: 12px;
  max-width: 34em;
  color: var(--silver);
  font-size: var(--fs-13);
  line-height: 1.75;
}

.footer__cols {
  display: grid;
  gap: var(--sp-24);
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
}
.footer__col-title {
  margin-bottom: 12px;
  font-family: var(--font-mono);
  font-size: var(--fs-13);
  font-weight: 500;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--silver);
}
.footer__links { display: grid; gap: var(--sp-8); }
.footer__links a {
  font-size: var(--fs-15);
  border-bottom: 1px solid transparent;
  transition: color var(--ease), border-color var(--ease);
}
.footer__links a:hover { color: var(--cyan); border-bottom-color: var(--cyan); }

.footer__contact { font-style: normal; }
.contact-row {
  display: flex;
  flex-wrap: wrap;
  gap: 4px 12px;
  padding: 8px 0;
  border-bottom: 1px dashed rgba(58, 74, 107, 0.7);
}
.contact-row__label {
  flex: 0 0 auto;
  min-width: 5em;
  color: var(--silver);
  font-size: var(--fs-13);
  letter-spacing: 0.05em;
}
.contact-row__value {
  font-family: var(--font-mono);
  font-size: 15px;
  color: var(--paper);
  letter-spacing: 0.02em;
  word-break: break-all;
}

.footer__legal {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 8px var(--sp-24);
  margin-top: var(--sp-40);
  padding-top: var(--sp-16);
  border-top: var(--line) solid var(--graphite);
}
.footer__legal-item {
  font-family: var(--font-mono);
  font-size: var(--fs-13);
  letter-spacing: 0.05em;
  color: var(--silver);
}

.to-top {
  position: fixed;
  right: 20px;
  bottom: 20px;
  z-index: 55;
  display: grid;
  place-items: center;
  width: 48px;
  height: 48px;
  background: var(--ink-800);
  border: var(--line) solid var(--graphite);
  color: var(--cyan);
  font-family: var(--font-mono);
  font-size: var(--fs-15);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(8px);
  transition: opacity var(--ease), transform var(--ease),
    visibility var(--ease), border-color var(--ease);
}
.to-top[data-visible="true"] {
  opacity: 1;
  visibility: visible;
  transform: none;
}
.to-top:hover { border-color: var(--cyan); background: var(--ink-700); }

/* ---------- 13. 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;
    scroll-behavior: auto !important;
  }
  .rail { transform: none; }
  .rail[data-open="false"] { transform: translateX(102%); }
  .to-top { transform: none; }
}