/* ==========================================================================
   site.css — 三亿体育入口 共享外壳与基础组件
   ========================================================================== */

*,
*::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, ul, ol, li, dl, dd, figure, blockquote {
  margin: 0;
}

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

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

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

:root {
  --ink: #061B18;
  --deep: #0B2B26;
  --card: #123D35;
  --line: #2C5A4F;
  --mint: #E7EFE8;
  --paper: #F6F2E8;
  --cyan: #18F0C4;
  --orange: #FF8A3D;
  --wine: #6E2336;
  --indigo: #3A2D6E;
  --mute: #9AAFA6;
  --mute-ink: #5E6F68;
  --warn: #FFD166;
  --ink-text: #10221D;

  --rail-w: 108px;
  --wrap: 1320px;
  --gut: clamp(16px, 3vw, 40px);

  --font-display: "Barlow Condensed", "Oswald", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  --font-body: "Noto Sans SC", "PingFang SC", "Microsoft YaHei", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --font-mono: "IBM Plex Mono", "JetBrains Mono", SFMono-Regular, ui-monospace, Consolas, "Courier New", monospace;

  --ease: cubic-bezier(0.2, 0.7, 0.2, 1);
  --t-fast: 150ms;
  --t-mid: 220ms;
  --t-slow: 380ms;
}

/* ---------- 基础排版 ---------- */

body {
  margin: 0;
  background: var(--ink);
  color: var(--mint);
  font-family: var(--font-body);
  font-size: 1rem;
  font-weight: 400;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
}

@media (min-width: 1080px) {
  body { padding-left: var(--rail-w); }
}

h1, h2, h3, h4 {
  font-family: var(--font-display);
  font-weight: 900;
  line-height: 1.12;
  letter-spacing: -0.02em;
  color: var(--mint);
}

h1 { font-size: clamp(2.4rem, 6vw, 5.6rem); letter-spacing: -0.03em; }
h2 { font-size: clamp(1.6rem, 3vw, 2.8rem); }
h3 { font-size: clamp(1.125rem, 1.6vw, 1.5rem); font-weight: 800; letter-spacing: -0.01em; }
h4 { font-size: 1rem; font-weight: 800; letter-spacing: -0.01em; }

p { max-width: 38em; }

a {
  color: var(--cyan);
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
}

::selection {
  background: var(--cyan);
  color: var(--ink);
}

:focus-visible {
  outline: 2px solid var(--cyan);
  outline-offset: 3px;
}

#main-content:focus { outline: none; }

/* ---------- 工具类 ---------- */

.mono {
  font-family: var(--font-mono);
  font-weight: 400;
  letter-spacing: 0.08em;
}

.container {
  width: 100%;
  max-width: var(--wrap);
  margin-inline: auto;
  padding-inline: var(--gut);
}

.container--narrow { max-width: 840px; }

.section { padding-block: clamp(40px, 6vw, 80px); }

.eyebrow {
  display: flex;
  align-items: center;
  gap: 10px;
  margin: 0 0 14px;
  font-family: var(--font-mono);
  font-size: 0.6875rem;
  font-weight: 400;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--cyan);
  max-width: none;
}

.eyebrow::before {
  content: "";
  flex: 0 0 auto;
  width: 20px;
  height: 1px;
  background: var(--cyan);
}

/* ---------- 按钮 ---------- */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 11px 20px;
  border: 1px solid transparent;
  border-radius: 0;
  background: transparent;
  color: var(--mint);
  font-family: var(--font-body);
  font-size: 0.875rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  line-height: 1.4;
  text-decoration: none;
  cursor: pointer;
  transition: background var(--t-fast) var(--ease),
              color var(--t-fast) var(--ease),
              border-color var(--t-fast) var(--ease),
              transform var(--t-fast) var(--ease);
}

.btn--primary {
  background: var(--orange);
  border-color: var(--orange);
  color: var(--ink-text);
}

.btn--primary:hover,
.btn--primary:focus-visible {
  background: var(--cyan);
  border-color: var(--cyan);
  color: var(--ink);
}

.btn--ghost {
  background: transparent;
  border-color: var(--line);
  color: var(--mint);
}

.btn--ghost:hover,
.btn--ghost:focus-visible {
  border-color: var(--cyan);
  color: var(--cyan);
}

.btn--sm {
  padding: 8px 14px;
  font-size: 0.8125rem;
}

/* ---------- 标签与卡片 ---------- */

.tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 10px;
  border: 1px solid var(--line);
  background: var(--card);
  color: var(--mint);
  font-family: var(--font-mono);
  font-size: 0.6875rem;
  letter-spacing: 0.08em;
  line-height: 1.6;
  text-decoration: none;
}

.tag--cyan { border-color: var(--cyan); color: var(--cyan); background: transparent; }
.tag--orange { background: var(--orange); border-color: var(--orange); color: var(--ink-text); }
.tag--wine { background: var(--wine); border-color: var(--wine); color: var(--paper); }
.tag--indigo { background: var(--indigo); border-color: var(--indigo); color: var(--mint); }

.cut-tag {
  display: inline-block;
  padding: 5px 16px 5px 10px;
  background: var(--orange);
  color: var(--ink-text);
  font-family: var(--font-mono);
  font-size: 0.6875rem;
  letter-spacing: 0.08em;
  line-height: 1.6;
  clip-path: polygon(0 0, 100% 0, calc(100% - 10px) 100%, 0 100%);
  transition: transform var(--t-fast) var(--ease);
}

.card {
  position: relative;
  background: var(--card);
  border: 1px solid var(--line);
  padding: clamp(18px, 2.4vw, 28px);
  color: var(--mint);
}

.card--paper {
  background: var(--paper);
  border-color: #CBD5CC;
  color: var(--ink-text);
}

.card--paper h3,
.card--paper h4 { color: var(--ink-text); }

.card--cut::before {
  content: "";
  position: absolute;
  top: -1px;
  left: -1px;
  width: 46px;
  height: 8px;
  background: var(--orange);
  clip-path: polygon(0 0, 100% 0, calc(100% - 8px) 100%, 0 100%);
  transition: transform var(--t-fast) var(--ease);
}

a.card {
  display: block;
  text-decoration: none;
  transition: border-color var(--t-fast) var(--ease);
}

a.card:hover,
a.card:focus-visible { border-color: var(--cyan); }

a.card:hover::before,
a.card:focus-visible::before { transform: translateX(3px); }

/* ---------- 网格 ---------- */

.grid {
  display: grid;
  gap: clamp(16px, 2.4vw, 32px);
}

.grid--2 { grid-template-columns: repeat(auto-fit, minmax(260px, 1fr)); }
.grid--3 { grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); }

/* ---------- 响应式图片容器 ---------- */

.media-frame {
  position: relative;
  display: block;
  width: 100%;
  aspect-ratio: 16 / 9;
  overflow: hidden;
  border: 1px solid var(--line);
  background:
    linear-gradient(160deg, rgba(24, 240, 196, 0.07), rgba(6, 27, 24, 0) 62%),
    var(--card);
}

.media-frame::after {
  content: "";
  position: absolute;
  inset: 0;
  z-index: 2;
  pointer-events: none;
  opacity: 0.55;
  background-image:
    linear-gradient(to right, rgba(44, 90, 79, 0.5) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(44, 90, 79, 0.5) 1px, transparent 1px);
  background-size: 32px 32px;
}

.media-frame img,
.media-frame picture,
.media-frame svg {
  position: relative;
  z-index: 1;
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.media-frame--square { aspect-ratio: 1 / 1; }
.media-frame--wide { aspect-ratio: 21 / 9; }
.media-frame--tall { aspect-ratio: 3 / 4; }

.media-frame--paper {
  background: var(--paper);
  border-color: #CBD5CC;
}

.media-frame--paper::after {
  background-image:
    linear-gradient(to right, rgba(94, 111, 104, 0.28) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(94, 111, 104, 0.28) 1px, transparent 1px);
}

/* ---------- 面包屑 ---------- */

.breadcrumb { margin: 0 0 24px; }

.breadcrumb__list {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  font-family: var(--font-mono);
  font-size: 0.6875rem;
  letter-spacing: 0.08em;
  color: var(--mute);
}

.breadcrumb__item {
  display: flex;
  align-items: center;
  gap: 8px;
}

.breadcrumb__item + .breadcrumb__item::before {
  content: "/";
  color: var(--line);
}

.breadcrumb__link {
  color: var(--mute);
  text-decoration: none;
  transition: color var(--t-fast) var(--ease);
}

.breadcrumb__link:hover,
.breadcrumb__link:focus-visible { color: var(--cyan); }

.breadcrumb__item[aria-current="page"] { color: var(--mint); }

/* ---------- 跳转链接 ---------- */

.skip-link {
  position: fixed;
  top: 10px;
  left: 10px;
  z-index: 200;
  padding: 10px 18px;
  background: var(--cyan);
  color: var(--ink);
  font-size: 0.875rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-decoration: none;
  transform: translateY(-180%);
  transition: transform var(--t-fast) var(--ease);
}

.skip-link:focus,
.skip-link:focus-visible {
  transform: translateY(0);
  outline: 2px solid var(--mint);
  outline-offset: 2px;
}

@media (min-width: 1080px) {
  .skip-link { left: calc(var(--rail-w) + 12px); }
}

/* ==========================================================================
   头部
   ========================================================================== */

.site-header {
  position: relative;
  z-index: 80;
}

/* 左侧品牌轨道 */
.rail { display: none; }

@media (min-width: 1080px) {
  .rail {
    position: fixed;
    inset: 0 auto 0 0;
    z-index: 90;
    display: flex;
    flex-direction: column;
    align-items: stretch;
    gap: 22px;
    width: var(--rail-w);
    padding: 20px 0 18px;
    background: var(--ink);
    border-right: 1px solid var(--line);
  }
}

.rail__brand {
  display: block;
  text-align: center;
  text-decoration: none;
  color: var(--mint);
}

.rail__mark {
  display: block;
  padding: 5px 0;
  font-family: var(--font-display);
  font-weight: 900;
  font-size: 1.0625rem;
  letter-spacing: 0.06em;
  line-height: 1.15;
  transition: color var(--t-fast) var(--ease);
}

.rail__mark--accent {
  color: var(--cyan);
  border-top: 1px solid var(--line);
}

.rail__brand:hover .rail__mark,
.rail__brand:focus-visible .rail__mark { color: var(--orange); }

.rail__brand:hover .rail__mark--accent,
.rail__brand:focus-visible .rail__mark--accent { color: var(--cyan); }

.rail__label {
  max-width: none;
  text-align: center;
  font-family: var(--font-mono);
  font-size: 0.625rem;
  letter-spacing: 0.2em;
  color: var(--mute);
  text-transform: uppercase;
  padding-inline: 8px;
}

.rail__seasons {
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}

.rail__seasons > li + li .rail__season {
  border-top: 1px solid rgba(44, 90, 79, 0.55);
}

.rail__season {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 2px;
  padding: 11px 0;
  color: var(--mute);
  text-decoration: none;
  transition: color var(--t-fast) var(--ease), background var(--t-fast) var(--ease);
}

.rail__season:hover,
.rail__season:focus-visible {
  color: var(--cyan);
  background: rgba(24, 240, 196, 0.07);
}

.rail__num {
  font-family: var(--font-mono);
  font-size: 0.8125rem;
  letter-spacing: 0.08em;
  line-height: 1.2;
}

.rail__tag {
  font-size: 0.625rem;
  letter-spacing: 0.16em;
  line-height: 1.2;
}

.rail__foot {
  margin-top: auto;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 8px;
  padding-inline: 8px;
  text-align: center;
}

.rail__foot-text {
  font-family: var(--font-mono);
  font-size: 0.625rem;
  letter-spacing: 0.14em;
  color: var(--mute);
}

/* 状态点 */
.status-dot {
  display: inline-block;
  flex: 0 0 auto;
  width: 6px;
  height: 6px;
  background: var(--cyan);
  box-shadow: 0 0 0 3px rgba(24, 240, 196, 0.16);
}

/* 上层信息带 */
.topline {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 8px var(--gut);
  background: var(--ink);
  border-bottom: 1px solid var(--line);
  color: var(--mute);
}

.topline__tagline {
  max-width: none;
  font-size: 0.75rem;
  letter-spacing: 0.08em;
  line-height: 1.6;
  color: var(--mute);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.topline__meta {
  display: flex;
  align-items: center;
  gap: 16px;
  flex: 0 0 auto;
}

.chip {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding: 3px 9px;
  border: 1px solid var(--line);
  background: transparent;
  color: var(--mint);
  font-family: var(--font-mono);
  font-size: 0.6875rem;
  letter-spacing: 0.08em;
  line-height: 1.6;
  white-space: nowrap;
}

.topline__icp {
  font-family: var(--font-mono);
  font-size: 0.6875rem;
  letter-spacing: 0.06em;
  color: var(--mute);
  white-space: nowrap;
}

/* 下层栏目带 */
.nav-band {
  position: relative;
  display: flex;
  align-items: center;
  gap: clamp(16px, 2.4vw, 40px);
  min-height: 64px;
  padding: 0 var(--gut);
  background: var(--deep);
  border-bottom: 1px solid var(--line);
}

@media (min-width: 900px) {
  .nav-band {
    position: sticky;
    top: 0;
    z-index: 70;
  }
}

.nav-band__brand {
  display: flex;
  flex-direction: column;
  justify-content: center;
  flex: 0 0 auto;
  padding: 6px 0;
  color: var(--mint);
  text-decoration: none;
}

.nav-band__title {
  font-family: var(--font-display);
  font-weight: 900;
  font-size: 1.0625rem;
  letter-spacing: -0.01em;
  line-height: 1.15;
  transition: color var(--t-fast) var(--ease);
}

.nav-band__brand:hover .nav-band__title,
.nav-band__brand:focus-visible .nav-band__title { color: var(--cyan); }

.nav-band__sub {
  font-family: var(--font-mono);
  font-size: 0.5625rem;
  letter-spacing: 0.24em;
  line-height: 1.4;
  color: var(--cyan);
  text-transform: uppercase;
}

.primary-nav {
  display: flex;
  align-items: center;
  gap: clamp(16px, 2vw, 32px);
  flex: 1 1 auto;
  min-width: 0;
}

.primary-nav__list {
  display: flex;
  align-items: center;
  gap: clamp(12px, 1.8vw, 28px);
  flex: 1 1 auto;
  justify-content: flex-start;
}

.primary-nav__link {
  display: inline-block;
  position: relative;
  padding: 8px 2px;
  border-bottom: 2px solid transparent;
  color: var(--mint);
  font-size: 0.9375rem;
  font-weight: 500;
  letter-spacing: 0.02em;
  line-height: 1.5;
  white-space: nowrap;
  text-decoration: none;
  transition: color var(--t-fast) var(--ease), border-color var(--t-fast) var(--ease);
}

.primary-nav__link:hover,
.primary-nav__link:focus-visible {
  color: var(--cyan);
  border-bottom-color: var(--line);
}

.primary-nav__link[aria-current="page"] {
  color: var(--cyan);
  font-weight: 700;
  border-bottom-color: var(--cyan);
}

.primary-nav__cta { flex: 0 0 auto; }

/* 移动菜单按钮 */
.nav-toggle {
  display: none;
  align-items: center;
  gap: 10px;
  margin-left: auto;
  padding: 10px 14px;
  border: 1px solid var(--line);
  background: transparent;
  color: var(--mint);
  font-family: var(--font-mono);
  font-size: 0.6875rem;
  letter-spacing: 0.14em;
  cursor: pointer;
  transition: border-color var(--t-fast) var(--ease), color var(--t-fast) var(--ease);
}

.nav-toggle:hover,
.nav-toggle:focus-visible {
  border-color: var(--cyan);
  color: var(--cyan);
}

.nav-toggle__box {
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 4px;
  width: 16px;
  height: 16px;
}

.nav-toggle__box span {
  display: block;
  width: 100%;
  height: 1.5px;
  background: currentColor;
  transition: transform var(--t-mid) var(--ease), opacity var(--t-fast) var(--ease);
}

.nav-toggle[aria-expanded="true"] .nav-toggle__box span:nth-child(1) {
  transform: translateY(5.5px) rotate(45deg);
}

.nav-toggle[aria-expanded="true"] .nav-toggle__box span:nth-child(2) {
  opacity: 0;
}

.nav-toggle[aria-expanded="true"] .nav-toggle__box span:nth-child(3) {
  transform: translateY(-5.5px) rotate(-45deg);
}

@media (max-width: 899px) {
  .nav-toggle { display: inline-flex; }

  .primary-nav {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    z-index: 60;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    max-height: 0;
    overflow: hidden;
    background: var(--deep);
    border-top: 1px solid transparent;
    border-bottom: 1px solid transparent;
    transition: max-height var(--t-mid) var(--ease), border-color var(--t-mid) linear;
  }

  .primary-nav[data-open] {
    max-height: min(78vh, 580px);
    overflow-y: auto;
    border-top-color: var(--line);
    border-bottom-color: var(--line);
  }

  .primary-nav__list {
    flex-direction: column;
    align-items: stretch;
    justify-content: flex-start;
    gap: 0;
  }

  .primary-nav__item + .primary-nav__item {
    border-top: 1px solid rgba(44, 90, 79, 0.55);
  }

  .primary-nav__link {
    display: block;
    padding: 14px var(--gut);
    border-bottom: 0;
    border-left: 2px solid transparent;
    font-size: 1rem;
  }

  .primary-nav__link:hover,
  .primary-nav__link:focus-visible {
    background: rgba(24, 240, 196, 0.06);
    border-left-color: var(--line);
  }

  .primary-nav__link[aria-current="page"] {
    background: rgba(24, 240, 196, 0.09);
    border-left-color: var(--cyan);
    border-bottom-color: transparent;
  }

  .primary-nav__cta {
    margin: 16px var(--gut) 22px;
    width: auto;
  }

  .topline__tagline { display: none; }
  .topline__meta { margin-left: auto; }
}

@media (max-width: 520px) {
  .topline { padding-block: 6px; }
  .topline__icp { display: none; }
  .chip { font-size: 0.625rem; padding: 2px 7px; }
}

/* ==========================================================================
   页脚
   ========================================================================== */

.site-footer {
  position: relative;
  margin-top: clamp(48px, 8vw, 96px);
  background: var(--ink);
  color: var(--mute);
  border-top: 1px solid var(--line);
}

.footer__top {
  padding: clamp(40px, 6vw, 72px) var(--gut) clamp(28px, 4vw, 44px);
}

.footer__grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: clamp(28px, 4vw, 48px);
  max-width: var(--wrap);
  margin-inline: auto;
}

@media (min-width: 640px) {
  .footer__grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (min-width: 1024px) {
  .footer__grid {
    grid-template-columns: minmax(0, 1.5fr) minmax(0, 0.9fr) minmax(0, 0.9fr) minmax(0, 1.7fr);
  }

  .footer__col,
  .footer__contact {
    padding-left: clamp(16px, 2vw, 28px);
    border-left: 1px solid var(--line);
  }
}

.footer__logo {
  display: inline-block;
  margin-bottom: 16px;
  padding-bottom: 5px;
  border-bottom: 2px solid var(--cyan);
  color: var(--mint);
  font-family: var(--font-display);
  font-weight: 900;
  font-size: 1.25rem;
  letter-spacing: -0.01em;
  line-height: 1.2;
  text-decoration: none;
  transition: color var(--t-fast) var(--ease), border-color var(--t-fast) var(--ease);
}

.footer__logo:hover,
.footer__logo:focus-visible {
  color: var(--cyan);
  border-bottom-color: var(--orange);
}

.footer__summary {
  max-width: 34em;
  font-size: 0.875rem;
  line-height: 1.85;
  color: var(--mute);
}

.footer__stamp {
  margin-top: 18px;
  font-family: var(--font-mono);
  font-size: 0.6875rem;
  letter-spacing: 0.1em;
  color: var(--mute);
}

.footer__col-title {
  margin: 0 0 16px;
  padding-top: 10px;
  border-top: 1px solid var(--line);
  font-family: var(--font-mono);
  font-weight: 500;
  font-size: 0.6875rem;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--cyan);
}

.footer__list {
  display: grid;
  gap: 11px;
}

.footer__link {
  color: var(--mint);
  font-size: 0.875rem;
  line-height: 1.6;
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: color var(--t-fast) var(--ease), border-color var(--t-fast) var(--ease);
}

.footer__link:hover,
.footer__link:focus-visible {
  color: var(--cyan);
  border-bottom-color: var(--line);
}

.footer__list--plain { gap: 12px; }

.footer__list--plain > li {
  display: grid;
  grid-template-columns: 52px minmax(0, 1fr);
  gap: 12px;
  align-items: start;
}

.footer__k {
  font-family: var(--font-mono);
  font-size: 0.6875rem;
  letter-spacing: 0.1em;
  color: var(--mute);
  line-height: 1.7;
}

.footer__v {
  font-size: 0.8125rem;
  line-height: 1.7;
  color: var(--mint);
  word-break: break-word;
}

.footer__note {
  max-width: 34em;
  margin-top: 18px;
  padding-top: 16px;
  border-top: 1px solid rgba(44, 90, 79, 0.6);
  font-size: 0.75rem;
  line-height: 1.8;
  color: var(--mute);
}

.footer__base {
  position: relative;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 10px 24px;
  padding: 22px var(--gut);
  border-top: 1px solid var(--line);
  background: var(--ink);
}

.footer__base::before {
  content: "";
  position: absolute;
  top: 1px;
  left: 0;
  right: 0;
  height: 6px;
  opacity: 0.7;
  background-image: repeating-linear-gradient(90deg, var(--line) 0 1px, transparent 1px 14px);
  pointer-events: none;
}

.footer__copy,
.footer__meta {
  max-width: none;
  font-size: 0.75rem;
  line-height: 1.7;
  color: var(--mute);
}

.footer__meta {
  font-family: var(--font-mono);
  letter-spacing: 0.06em;
}

/* ---------- 返回顶部 ---------- */

.to-top {
  position: fixed;
  right: clamp(12px, 2vw, 24px);
  bottom: clamp(12px, 2vw, 24px);
  z-index: 100;
  display: grid;
  place-items: center;
  width: 44px;
  height: 44px;
  padding: 0;
  border: 1px solid var(--line);
  background: var(--card);
  color: var(--cyan);
  font-family: var(--font-mono);
  font-size: 1rem;
  line-height: 1;
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(10px);
  transition: opacity var(--t-mid) var(--ease),
              transform var(--t-mid) var(--ease),
              visibility var(--t-mid) linear,
              border-color var(--t-fast) var(--ease),
              color var(--t-fast) var(--ease),
              background var(--t-fast) var(--ease);
}

.to-top[data-visible] {
  opacity: 1;
  visibility: visible;
  transform: none;
}

.to-top:hover,
.to-top:focus-visible {
  background: var(--deep);
  border-color: var(--cyan);
  color: var(--mint);
}

/* ---------- 滚动显现 ---------- */

[data-reveal] {
  transition: opacity var(--t-slow) var(--ease), transform var(--t-slow) var(--ease);
}

html.js-reveal [data-reveal]:not([data-revealed]) {
  opacity: 0;
  transform: translateY(14px);
}

html.js-reveal [data-reveal][data-revealed] {
  opacity: 1;
  transform: none;
}

/* ---------- 减少动态效果 ---------- */

@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;
  }

  [data-reveal] {
    opacity: 1 !important;
    transform: none !important;
  }

  .skip-link { transition: none; }

  .to-top {
    transition: opacity 0.001ms, visibility 0.001ms;
    transform: none;
  }
}