/* ===== 365平台中心 · 共享样式 /assets/site.css ===== */

/* --- 1. Reset --- */
*,
*::before,
*::after { box-sizing: border-box; }
html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: 132px;
}
body, h1, h2, h3, h4, p, ul, ol, figure, blockquote, dl, dd { margin: 0; }
ul, ol { padding: 0; list-style: none; }
img, svg { max-width: 100%; }
button, input, select, textarea { font: inherit; color: inherit; }

/* --- 2. 变量 --- */
:root {
  --ink: #0A1523;
  --ink-deep: #070F1B;
  --panel: #12263A;
  --line: #24405A;
  --paper: #F4EFE4;
  --muted: #A9B7C4;
  --amber: #E5A13C;
  --amber-deep: #B9761F;
  --celadon: #5FA08D;
  --cyan: #3FE0CF;
  --brick: #D2653F;

  --shell: 1200px;
  --pad: clamp(20px, 5vw, 64px);

  --serif: "Noto Serif SC", "Source Han Serif SC", Georgia, "Times New Roman", serif;
  --sans: "Noto Sans SC", "PingFang SC", "Microsoft YaHei", system-ui, -apple-system, sans-serif;
  --cond: "Barlow Condensed", "Oswald", "Noto Sans SC", system-ui, sans-serif;
  --mono: "JetBrains Mono", "SFMono-Regular", Consolas, "Courier New", monospace;

  --ease: cubic-bezier(.2, .7, .3, 1);
  --dur: 260ms;
}

/* --- 3. 基础排版 --- */
body {
  min-height: 100vh;
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.85;
  color: var(--paper);
  background:
    radial-gradient(1200px 620px at 82% -8%, rgba(229, 161, 60, .075), transparent 68%),
    radial-gradient(900px 520px at -8% 18%, rgba(95, 160, 141, .06), transparent 70%),
    var(--ink);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}
body[data-nav-open] { overflow: hidden; }
h1, h2, h3 { font-family: var(--serif); font-weight: 600; line-height: 1.2; }
a { color: var(--amber); text-decoration-thickness: 1px; text-underline-offset: 3px; }
::selection { background: var(--amber); color: #171008; }
:focus-visible {
  outline: 2px solid var(--amber);
  outline-offset: 3px;
  border-radius: 1px;
}

/* --- 4. 容器 / 栅格 --- */
.shell {
  width: 100%;
  max-width: var(--shell);
  margin-inline: auto;
  padding-inline: var(--pad);
}
.grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: clamp(20px, 3vw, 40px);
}
@media (min-width: 900px) {
  .grid--split { grid-template-columns: 5fr 7fr; }
  .grid--aside { grid-template-columns: 3fr 9fr; }
  .grid--halves { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

/* --- 5. 跳转链接 --- */
.skip-link {
  position: absolute;
  top: -80px;
  left: 16px;
  z-index: 999;
  padding: 10px 18px;
  font-family: var(--cond);
  font-size: 14px;
  letter-spacing: .1em;
  color: #171008;
  background: var(--amber);
  border-radius: 2px;
  text-decoration: none;
  transition: top var(--dur) var(--ease);
}
.skip-link:focus { top: 12px; }

/* --- 6. 页头 --- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 120;
  background: var(--ink);
  border-bottom: 1px solid var(--line);
}

/* 6.1 认证信息带 */
.header-utility {
  background: var(--ink-deep);
  border-bottom: 1px solid var(--line);
  overflow: hidden;
  max-height: 64px;
  transition: max-height var(--dur) var(--ease), opacity 200ms linear;
}
.header-utility__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  min-height: 38px;
  padding-block: 4px;
}
.cert-mark {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  font-family: var(--cond);
  font-size: 13px;
  letter-spacing: .14em;
  color: var(--amber);
  white-space: nowrap;
}
.cert-mark__dot {
  width: 7px;
  height: 7px;
  background: var(--amber);
  transform: rotate(45deg);
  box-shadow: 0 0 0 3px rgba(229, 161, 60, .16);
}
.quick-links {
  display: flex;
  align-items: center;
  gap: 22px;
  margin-inline-start: auto;
}
.quick-links__item {
  font-family: var(--cond);
  font-size: 13px;
  letter-spacing: .1em;
  color: var(--muted);
  text-decoration: none;
  padding-bottom: 2px;
  border-bottom: 1px solid transparent;
  transition: color var(--dur) var(--ease), border-color var(--dur) var(--ease);
}
.quick-links__item:hover,
.quick-links__item:focus-visible {
  color: var(--paper);
  border-bottom-color: var(--amber);
}

/* 6.2 主栏 */
.header-band { position: relative; background: var(--ink); }
.header-band__inner {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 32px;
  min-height: 86px;
  transition: min-height var(--dur) var(--ease);
}
.brand {
  display: inline-flex;
  align-items: center;
  gap: 14px;
  text-decoration: none;
  color: var(--paper);
  flex-shrink: 0;
}
.brand__mark {
  font-family: var(--serif);
  font-size: 24px;
  font-weight: 600;
  line-height: 1;
  letter-spacing: .02em;
  color: var(--amber);
  padding: 8px 10px;
  border: 1px solid var(--line);
  background: var(--panel);
  border-radius: 2px;
  transition: border-color var(--dur) var(--ease);
}
.brand:hover .brand__mark { border-color: var(--amber); }
.brand__text { display: block; }
.brand__name {
  display: block;
  font-family: var(--serif);
  font-size: 17px;
  font-weight: 600;
  letter-spacing: .05em;
  line-height: 1.4;
}
.brand__sub {
  display: block;
  font-family: var(--cond);
  font-size: 11.5px;
  letter-spacing: .2em;
  color: var(--muted);
  line-height: 1.4;
  transition: opacity 200ms linear;
}

/* 6.3 主导航 */
.primary-nav__list {
  display: flex;
  align-items: center;
  gap: clamp(12px, 1.8vw, 26px);
}
.primary-nav__link {
  position: relative;
  display: inline-flex;
  align-items: baseline;
  gap: 6px;
  padding: 8px 2px;
  font-family: var(--cond);
  font-size: 15px;
  letter-spacing: .1em;
  color: var(--muted);
  text-decoration: none;
  white-space: nowrap;
  transition: color var(--dur) var(--ease);
}
.primary-nav__num {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0;
  color: var(--line);
  transition: color var(--dur) var(--ease);
}
.primary-nav__link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 100%;
  bottom: 0;
  height: 2px;
  background: var(--amber);
  transition: right var(--dur) var(--ease);
}
.primary-nav__link:hover,
.primary-nav__link:focus-visible { color: var(--paper); }
.primary-nav__link:hover .primary-nav__num,
.primary-nav__link:focus-visible .primary-nav__num { color: var(--amber); }
.primary-nav__link:hover::after,
.primary-nav__link:focus-visible::after { right: 0; }
.primary-nav__link[aria-current="page"] { color: var(--amber); }
.primary-nav__link[aria-current="page"] .primary-nav__num { color: var(--amber); }
.primary-nav__link[aria-current="page"]::after { right: 0; }
.primary-nav__foot { display: none; }

/* 6.4 移动端按钮 */
.nav-toggle {
  display: none;
  align-items: center;
  gap: 10px;
  padding: 9px 14px;
  background: transparent;
  border: 1px solid var(--line);
  border-radius: 2px;
  color: var(--paper);
  font-family: var(--cond);
  font-size: 14px;
  letter-spacing: .14em;
  cursor: pointer;
  transition: border-color var(--dur) var(--ease), color var(--dur) var(--ease);
}
.nav-toggle:hover { border-color: var(--amber); color: var(--amber); }
.nav-toggle__glyph { display: grid; gap: 4px; width: 16px; }
.nav-toggle__bar {
  display: block;
  height: 1.5px;
  width: 100%;
  background: var(--amber);
  border-radius: 1px;
  transition: transform var(--dur) var(--ease), opacity 180ms linear;
}

/* 6.5 遮罩 */
.nav-scrim {
  position: fixed;
  inset: 0;
  z-index: 190;
  background: rgba(4, 10, 18, .72);
  opacity: 0;
  pointer-events: none;
  transition: opacity var(--dur) var(--ease);
}
.site-header[data-open="true"] .nav-scrim {
  opacity: 1;
  pointer-events: auto;
}

/* 6.6 滚动进度尺 */
.scroll-meter {
  position: absolute;
  left: 0;
  bottom: 0;
  width: 100%;
  height: 2px;
  transform: scaleX(0);
  transform-origin: 0 50%;
  background: linear-gradient(90deg, var(--amber), var(--amber-deep));
  transition: transform 120ms linear;
}

/* 6.7 收拢态 */
.site-header.is-condensed .header-utility {
  max-height: 0;
  opacity: 0;
  border-bottom-color: transparent;
}
.site-header.is-condensed .header-band__inner { min-height: 58px; }
.site-header.is-condensed .brand__sub { opacity: 0; }

/* 6.8 移动端抽屉 */
@media (max-width: 980px) {
  html { scroll-padding-top: 96px; }
  .nav-toggle { display: inline-flex; }
  .header-utility__inner { min-height: 34px; gap: 14px; }
  .quick-links { display: none; }
  .header-band__inner { min-height: 64px; gap: 16px; }
  .brand__sub { display: none; }

  .primary-nav {
    position: fixed;
    top: 0;
    bottom: 0;
    left: 0;
    z-index: 200;
    display: flex;
    flex-direction: column;
    gap: 26px;
    width: min(324px, 84vw);
    padding: 92px 24px 28px;
    overflow-y: auto;
    background: var(--panel);
    border-right: 1px solid var(--line);
    box-shadow: 24px 0 60px rgba(3, 8, 16, .6);
    transform: translateX(-102%);
    transition: transform 300ms var(--ease);
    visibility: hidden;
  }
  .site-header[data-open="true"] .primary-nav {
    transform: translateX(0);
    visibility: visible;
  }
  .primary-nav__list {
    display: flex;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
  }
  .primary-nav__link {
    display: flex;
    align-items: baseline;
    gap: 12px;
    padding: 14px 2px;
    font-size: 17px;
    color: var(--paper);
    border-bottom: 1px solid var(--line);
  }
  .primary-nav__link::after { display: none; }
  .primary-nav__link[aria-current="page"] {
    color: var(--amber);
    padding-left: 12px;
    border-left: 2px solid var(--amber);
    border-bottom-color: rgba(229, 161, 60, .38);
  }
  .primary-nav__num { font-size: 11px; color: var(--celadon); }
  .primary-nav__foot {
    display: flex;
    flex-direction: column;
    gap: 10px;
    margin-top: auto;
    padding-top: 18px;
    border-top: 1px solid var(--line);
  }
  .primary-nav__footlink {
    display: block;
    padding: 12px 14px;
    font-size: 14px;
    letter-spacing: .04em;
    color: var(--paper);
    text-decoration: none;
    background: rgba(244, 239, 228, .035);
    border: 1px solid var(--line);
    border-left: 3px solid var(--celadon);
    border-radius: 2px;
    transition: background var(--dur) var(--ease), border-color var(--dur) var(--ease);
  }
  .primary-nav__footlink:first-child { border-left-color: var(--amber); }
  .primary-nav__footlink:hover { background: rgba(244, 239, 228, .08); }

  .site-header[data-open="true"] .nav-toggle__bar:nth-child(1) { transform: translateY(5.5px) rotate(45deg); }
  .site-header[data-open="true"] .nav-toggle__bar:nth-child(2) { opacity: 0; }
  .site-header[data-open="true"] .nav-toggle__bar:nth-child(3) { transform: translateY(-5.5px) rotate(-45deg); }
}

@media (max-width: 520px) {
  .header-utility .btn--tiny { padding: 5px 10px; font-size: 12px; }
  .cert-mark { font-size: 12px; letter-spacing: .1em; }
  .brand__name { font-size: 15.5px; }
  .brand__mark { font-size: 20px; padding: 7px 8px; }
  .nav-toggle__label { display: none; }
}

/* --- 7. 按钮 --- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 11px 22px;
  font-family: var(--cond);
  font-size: 14px;
  line-height: 1.2;
  letter-spacing: .12em;
  text-decoration: none;
  color: var(--paper);
  background: transparent;
  border: 1px solid var(--line);
  border-radius: 2px;
  cursor: pointer;
  transition: background var(--dur) var(--ease), color var(--dur) var(--ease),
              border-color var(--dur) var(--ease), transform 200ms var(--ease);
}
.btn--solid {
  color: #171008;
  background: linear-gradient(180deg, #EDB35C, var(--amber) 48%, var(--amber-deep));
  border-color: var(--amber-deep);
  font-weight: 600;
}
.btn--solid:hover { transform: translateY(-1px); }
.btn--solid:active { transform: translateY(0); }
.btn--ghost { color: var(--paper); background: transparent; border-color: var(--line); }
.btn--ghost:hover { color: var(--amber); border-color: var(--amber); }
.btn--tiny { padding: 6px 14px; font-size: 12.5px; letter-spacing: .1em; }
.btn--block { display: flex; width: 100%; }

/* --- 8. 标签 --- */
.tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 10px;
  font-family: var(--cond);
  font-size: 12.5px;
  letter-spacing: .1em;
  line-height: 1.6;
  color: var(--muted);
  background: rgba(244, 239, 228, .025);
  border: 1px solid var(--line);
  border-radius: 2px;
}
.tag--amber { color: var(--amber); border-color: rgba(229, 161, 60, .45); background: rgba(229, 161, 60, .09); }
.tag--celadon { color: var(--celadon); border-color: rgba(95, 160, 141, .45); background: rgba(95, 160, 141, .09); }
.tag--cyan { color: var(--cyan); border-color: rgba(63, 224, 207, .42); background: rgba(63, 224, 207, .08); }
.tag--outline { color: var(--paper); border-color: var(--line); }

/* --- 9. 面包屑 --- */
.crumb {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  font-family: var(--cond);
  font-size: 13px;
  letter-spacing: .08em;
  color: var(--muted);
  list-style: none;
  padding: 0;
  margin: 0;
}
.crumb li { display: inline-flex; align-items: center; gap: 8px; }
.crumb li + li::before { content: "／"; color: var(--line); }
.crumb a { color: var(--muted); text-decoration: none; transition: color var(--dur) var(--ease); }
.crumb a:hover { color: var(--amber); }

/* --- 10. 章节头 --- */
.section-head {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: clamp(14px, 3vw, 34px);
  align-items: start;
  padding-top: 16px;
  border-top: 1px solid var(--line);
}
.section-head__num {
  font-family: var(--serif);
  font-size: clamp(40px, 6vw, 88px);
  font-weight: 600;
  line-height: .88;
  letter-spacing: -.02em;
  color: var(--amber);
}
.section-head__title {
  font-family: var(--serif);
  font-size: clamp(23px, 3vw, 40px);
  font-weight: 600;
  line-height: 1.22;
  color: var(--paper);
}

/* --- 11. 正文容器 --- */
.prose {
  display: grid;
  gap: 18px;
  max-width: 720px;
  font-size: 16px;
  line-height: 1.85;
  color: var(--muted);
}
.prose h2 {
  margin-top: 14px;
  font-family: var(--serif);
  font-size: clamp(21px, 2.4vw, 28px);
  font-weight: 600;
  line-height: 1.35;
  color: var(--paper);
}
.prose h3 {
  margin-top: 6px;
  font-family: var(--serif);
  font-size: 19px;
  color: var(--paper);
}
.prose strong { color: var(--paper); font-weight: 600; }
.prose a { color: var(--amber); }
.prose ul { display: grid; gap: 8px; padding-left: 1.15em; list-style: disc; }
.prose ol { display: grid; gap: 8px; padding-left: 1.35em; list-style: decimal; }
.prose li::marker { color: var(--amber); font-family: var(--mono); font-size: 13px; }
.prose blockquote {
  padding-left: 18px;
  border-left: 2px solid var(--amber);
  font-family: var(--serif);
  font-size: 18px;
  line-height: 1.7;
  color: var(--paper);
}
.prose hr { width: 100%; border: 0; border-top: 1px solid var(--line); }

/* --- 12. 图片容器基础规则 --- */
.figure {
  display: grid;
  gap: 10px;
  max-width: 100%;
  margin: 0;
}
.figure__frame {
  position: relative;
  width: 100%;
  aspect-ratio: 16 / 10;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 2px;
  background-color: var(--panel);
  background-image:
    radial-gradient(120% 90% at 18% 8%, rgba(229, 161, 60, .14), transparent 62%),
    radial-gradient(100% 80% at 92% 100%, rgba(63, 224, 207, .1), transparent 60%),
    repeating-linear-gradient(0deg, rgba(36, 64, 90, .8) 0 1px, transparent 1px 26px);
}
.figure__frame img,
.figure__frame picture,
.figure__frame video {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
}
.figure__caption {
  padding-left: 10px;
  border-left: 2px solid var(--amber);
  font-family: var(--cond);
  font-size: 12.5px;
  line-height: 1.6;
  letter-spacing: .08em;
  color: var(--muted);
}
.figure--4x3 .figure__frame { aspect-ratio: 4 / 3; }
.figure--square .figure__frame { aspect-ratio: 1 / 1; }
.figure--tall .figure__frame { aspect-ratio: 3 / 4; }

/* --- 13. 页脚 --- */
.site-footer {
  margin-top: clamp(56px, 8vw, 104px);
  color: var(--muted);
  background: var(--ink-deep);
  border-top: 1px solid var(--line);
}

/* 13.1 品牌声明 */
.footer-statement {
  padding-block: clamp(40px, 6vw, 76px);
  border-bottom: 1px solid var(--line);
  background:
    radial-gradient(760px 320px at 12% 0%, rgba(229, 161, 60, .1), transparent 70%),
    linear-gradient(180deg, #0D1A2B, #0A1523);
}
.footer-statement__inner {
  display: grid;
  gap: 18px;
  grid-template-columns: minmax(0, 1fr);
}
.footer-statement__label {
  font-family: var(--cond);
  font-size: 13px;
  letter-spacing: .18em;
  color: var(--amber);
}
.footer-statement__text {
  max-width: 28em;
  font-family: var(--serif);
  font-size: clamp(20px, 2.6vw, 30px);
  font-weight: 600;
  line-height: 1.6;
  color: var(--paper);
}
@media (min-width: 900px) {
  .footer-statement__inner {
    grid-template-columns: 4fr 8fr;
    align-items: start;
    gap: 40px;
  }
}

/* 13.2 栏目索引 */
.footer-body {
  padding-block: clamp(36px, 5vw, 60px);
  border-bottom: 1px solid var(--line);
}
.footer-body__inner {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: clamp(28px, 4vw, 56px);
}
@media (min-width: 760px) {
  .footer-body__inner { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}
@media (min-width: 1000px) {
  .footer-body__inner { grid-template-columns: 1fr 1fr 1.35fr; }
}
.footer-title {
  margin-bottom: 16px;
  padding-bottom: 10px;
  font-family: var(--cond);
  font-size: 13px;
  font-weight: 600;
  letter-spacing: .2em;
  color: var(--paper);
  border-bottom: 1px solid var(--line);
}
.footer-links { display: grid; gap: 10px; }
.footer-links a {
  display: inline-block;
  padding-left: 2px;
  border-left: 2px solid transparent;
  font-size: 15px;
  color: var(--muted);
  text-decoration: none;
  transition: color var(--dur) var(--ease), padding-left var(--dur) var(--ease),
              border-color var(--dur) var(--ease);
}
.footer-links a:hover,
.footer-links a:focus-visible {
  padding-left: 8px;
  color: var(--paper);
  border-left-color: var(--amber);
}
.footer-entries { display: grid; gap: 12px; align-content: start; }
.footer-entry {
  display: grid;
  gap: 3px;
  padding: 13px 16px;
  text-decoration: none;
  background: rgba(244, 239, 228, .03);
  border: 1px solid var(--line);
  border-left: 3px solid var(--line);
  border-radius: 2px;
  transition: background var(--dur) var(--ease), border-color var(--dur) var(--ease),
              transform 200ms var(--ease);
}
.footer-entry--amber { border-left-color: var(--amber); }
.footer-entry--celadon { border-left-color: var(--celadon); }
.footer-entry:hover,
.footer-entry:focus-visible {
  background: rgba(244, 239, 228, .07);
  border-color: var(--line);
  transform: translateY(-1px);
}
.footer-entry__label {
  font-size: 15px;
  font-weight: 600;
  letter-spacing: .03em;
  color: var(--paper);
}
.footer-entry__hint {
  font-family: var(--cond);
  font-size: 12.5px;
  letter-spacing: .06em;
  color: var(--muted);
}

/* 13.3 联系方式 */
.footer-contact {
  padding-block: clamp(30px, 4vw, 48px);
  border-bottom: 1px solid var(--line);
}
.footer-contact__inner {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 22px 36px;
}
@media (min-width: 760px) {
  .footer-contact__inner { grid-template-columns: repeat(3, minmax(0, 1fr)); }
}
.footer-contact__item {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  align-items: center;
  gap: 4px 10px;
}
.footer-contact__label {
  grid-column: 1 / -1;
  font-family: var(--cond);
  font-size: 12px;
  letter-spacing: .16em;
  color: var(--celadon);
}
.footer-contact__value {
  font-family: var(--mono);
  font-size: 13.5px;
  line-height: 1.7;
  color: var(--paper);
  word-break: break-all;
}
.copy-btn {
  padding: 3px 9px;
  font-family: var(--cond);
  font-size: 12px;
  letter-spacing: .1em;
  color: var(--muted);
  background: transparent;
  border: 1px solid var(--line);
  border-radius: 2px;
  cursor: pointer;
  transition: color var(--dur) var(--ease), border-color var(--dur) var(--ease),
              background var(--dur) var(--ease);
}
.copy-btn:hover,
.copy-btn:focus-visible { color: var(--amber); border-color: var(--amber); }
.copy-btn.is-copied { color: var(--ink); background: var(--celadon); border-color: var(--celadon); }
.footer-contact__note {
  grid-column: 1 / -1;
  font-size: 13px;
  line-height: 1.8;
  color: var(--muted);
}
.footer-icp {
  grid-column: 1 / -1;
  font-family: var(--mono);
  font-size: 12.5px;
  letter-spacing: .04em;
  color: var(--line);
}

/* 13.4 版权行 */
.footer-bottom { padding-block: 20px; }
.footer-bottom__inner {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 12px 28px;
}
.footer-copy {
  font-family: var(--mono);
  font-size: 12.5px;
  letter-spacing: .04em;
  color: var(--muted);
}
.footer-legal { display: flex; flex-wrap: wrap; gap: 8px 22px; }
.footer-legal a {
  font-family: var(--cond);
  font-size: 13px;
  letter-spacing: .1em;
  color: var(--muted);
  text-decoration: none;
  transition: color var(--dur) var(--ease);
}
.footer-legal a:hover,
.footer-legal a:focus-visible { color: var(--amber); }

/* --- 14. 返回顶部（由 JS 注入） --- */
.to-top {
  position: fixed;
  right: clamp(16px, 3vw, 32px);
  bottom: clamp(16px, 3vw, 32px);
  z-index: 150;
  width: 46px;
  height: 46px;
  display: grid;
  place-items: center;
  font-family: var(--mono);
  font-size: 16px;
  color: var(--amber);
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 2px;
  box-shadow: 0 8px 24px rgba(3, 8, 16, .55);
  cursor: pointer;
  opacity: 0;
  pointer-events: none;
  transform: translateY(10px);
  transition: opacity var(--dur) var(--ease), transform var(--dur) var(--ease),
              border-color var(--dur) var(--ease);
}
.to-top.is-visible { opacity: 1; pointer-events: auto; transform: translateY(0); }
.to-top:hover { border-color: var(--amber); }

/* --- 15. 无障碍降级 --- */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *,
  *::before,
  *::after {
    animation-duration: .001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: .001ms !important;
    scroll-behavior: auto !important;
  }
}