/* =========================================================
   欧云游艺 · 共享样式 /assets/site.css
   深空蓝底 × 霓虹青光轨 × 奶油纸白实色层
   ========================================================= */

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

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  background-color: #0B1026;
}

body {
  margin: 0;
  background: transparent;
  color: #F4EFE3;
  font-family: var(--font-body);
  font-size: clamp(16px, 0.32vw + 14.6px, 17.5px);
  line-height: 1.75;
  letter-spacing: 0.01em;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

img, svg, video { max-width: 100%; height: auto; display: block; }
button { font: inherit; color: inherit; }
a { color: inherit; }
ul, ol { margin: 0; padding: 0; list-style: none; }
p { margin: 0 0 1em; }
p:last-child { margin-bottom: 0; }

h1, h2, h3, h4 {
  margin: 0 0 0.6em;
  font-family: var(--font-display);
  font-weight: 800;
  letter-spacing: -0.02em;
  line-height: 1.14;
  color: #F4EFE3;
}

[id] { scroll-margin-top: clamp(96px, 13vh, 150px); }

/* ---------- 2. 设计令牌 ---------- */
:root {
  /* 色板 */
  --deep-space: #0B1026;
  --night-blue: #131A3A;
  --neon-cyan: #35E6E0;
  --violet: #8B5CF6;
  --warm-orange: #FF8A3D;
  --cream: #F4EFE3;
  --ink: #241C16;
  --stardust: #9AA3C0;
  --aurora-pink: #FF6FB5;
  --lime: #7BE495;

  /* 语义 */
  --bg: var(--deep-space);
  --surface: var(--night-blue);
  --text: var(--cream);
  --text-muted: var(--stardust);
  --line: rgba(154, 163, 192, 0.18);
  --line-strong: rgba(154, 163, 192, 0.32);
  --line-cyan: rgba(53, 230, 224, 0.24);
  --glass: rgba(19, 26, 58, 0.55);

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

  /* 尺度 */
  --shell: 1240px;
  --gutter: clamp(18px, 4vw, 40px);
  --radius-s: 10px;
  --radius-m: 18px;
  --radius-l: 28px;
  --ease: cubic-bezier(0.2, 0.7, 0.3, 1);
}

/* ---------- 3. 全局背景层：极光 + 光轨 ---------- */
body::before {
  content: "";
  position: fixed;
  inset: -12%;
  z-index: -1;
  pointer-events: none;
  background:
    radial-gradient(900px 620px at 84% -8%, rgba(139, 92, 246, 0.26), transparent 68%),
    radial-gradient(720px 520px at 6% 14%, rgba(53, 230, 224, 0.16), transparent 68%),
    radial-gradient(900px 700px at 52% 108%, rgba(255, 111, 181, 0.11), transparent 70%),
    radial-gradient(600px 420px at 96% 62%, rgba(255, 138, 61, 0.09), transparent 72%);
  animation: aurora-drift 19s ease-in-out infinite;
}

@keyframes aurora-drift {
  0%, 100% { transform: translate3d(0, 0, 0) scale(1); }
  50%      { transform: translate3d(-1.6%, 1.4%, 0) scale(1.05); }
}

/* ---------- 4. 布局基础 ---------- */
.container {
  width: 100%;
  max-width: var(--shell);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.section {
  position: relative;
  padding-block: clamp(48px, 7vw, 96px);
}

.section-head {
  display: grid;
  gap: 12px;
  max-width: 760px;
  margin-bottom: clamp(26px, 4vw, 52px);
}

.section-head--center {
  margin-inline: auto;
  text-align: center;
  justify-items: center;
}

.stack { display: grid; gap: clamp(16px, 2vw, 26px); }

.grid-2,
.grid-3 { display: grid; gap: clamp(18px, 3vw, 36px); }
.grid-2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.grid-3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }

/* ---------- 5. 文字组件 ---------- */
.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-family: var(--font-mono);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--neon-cyan);
}

.eyebrow::before {
  content: "";
  width: 26px;
  height: 1px;
  background: currentColor;
}

.lede {
  max-width: 62ch;
  font-size: clamp(16.5px, 1.1vw + 13px, 20px);
  line-height: 1.72;
  color: #E7E2D6;
}

.meta {
  font-family: var(--font-mono);
  font-size: 12.5px;
  font-weight: 600;
  letter-spacing: 0.08em;
  color: var(--stardust);
}

.num {
  display: inline-block;
  padding: 0.08em 0.44em;
  border-radius: 6px;
  background: rgba(53, 230, 224, 0.13);
  border: 1px solid rgba(53, 230, 224, 0.3);
  color: var(--neon-cyan);
  font-family: var(--font-mono);
  font-weight: 700;
  letter-spacing: 0;
}

/* ---------- 6. 按钮 ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 11px 18px;
  border: 1px solid transparent;
  border-radius: 999px;
  font-family: var(--font-display);
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 0.06em;
  line-height: 1;
  text-decoration: none;
  white-space: nowrap;
  cursor: pointer;
  transition: transform 0.3s var(--ease), background-color 0.3s ease,
              color 0.3s ease, border-color 0.3s ease, box-shadow 0.3s ease;
}

.btn:hover { transform: translateY(-2px); }
.btn:active { transform: translateY(0); }

.btn--neon {
  color: #04161A;
  background: linear-gradient(118deg, #35E6E0 0%, #79F4FF 100%);
  box-shadow: 0 0 0 1px rgba(53, 230, 224, 0.55), 0 14px 30px -16px rgba(53, 230, 224, 0.95);
}

.btn--neon:hover {
  box-shadow: 0 0 0 1px rgba(53, 230, 224, 0.9), 0 18px 36px -14px rgba(53, 230, 224, 1);
}

.btn--ghost {
  color: var(--cream);
  background: rgba(244, 239, 227, 0.05);
  border-color: rgba(244, 239, 227, 0.3);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
}

.btn--ghost:hover {
  border-color: var(--neon-cyan);
  color: var(--neon-cyan);
  background: rgba(53, 230, 224, 0.09);
}

.btn--orange {
  color: #1B0C01;
  background: linear-gradient(118deg, #FF8A3D 0%, #FFB273 100%);
  box-shadow: 0 14px 30px -16px rgba(255, 138, 61, 0.95);
}

.btn--orange:hover { box-shadow: 0 18px 36px -14px rgba(255, 138, 61, 1); }

/* ---------- 7. 卡片 ---------- */
.card {
  position: relative;
  padding: clamp(20px, 2.6vw, 30px);
  border: 1px solid var(--line);
  border-radius: var(--radius-m);
  background: linear-gradient(170deg, rgba(19, 26, 58, 0.94), rgba(11, 16, 38, 0.94));
  overflow: hidden;
  transition: transform 0.35s var(--ease), border-color 0.35s ease, box-shadow 0.35s ease;
}

.card::before {
  content: "";
  position: absolute;
  inset: 0 0 auto 0;
  height: 2px;
  background: linear-gradient(90deg, var(--neon-cyan), var(--violet) 55%, transparent);
  opacity: 0.75;
}

.card:hover {
  transform: translateY(-5px);
  border-color: var(--line-cyan);
  box-shadow: 0 26px 60px -34px rgba(53, 230, 224, 0.7);
}

.card--glass {
  background: var(--glass);
  border-color: rgba(244, 239, 227, 0.16);
  backdrop-filter: blur(16px) saturate(140%);
  -webkit-backdrop-filter: blur(16px) saturate(140%);
}

.card--cream {
  background: var(--cream);
  border-color: rgba(36, 28, 22, 0.14);
  color: var(--ink);
}

.card--cream::before {
  background: linear-gradient(90deg, var(--warm-orange), var(--violet) 60%, transparent);
}

.card--cream h1,
.card--cream h2,
.card--cream h3,
.card--cream h4 { color: var(--ink); }

/* ---------- 8. 图片容器（页面阶段复用） ---------- */
.media-frame {
  position: relative;
  display: block;
  width: 100%;
  aspect-ratio: 16 / 10;
  margin: 0;
  overflow: hidden;
  border: 1px solid rgba(139, 92, 246, 0.32);
  border-radius: var(--radius-m);
  background:
    linear-gradient(135deg, rgba(139, 92, 246, 0.3) 0%, rgba(53, 230, 224, 0.16) 48%, rgba(255, 138, 61, 0.16) 100%),
    var(--night-blue);
  isolation: isolate;
}

.media-frame::after {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  background: repeating-linear-gradient(
    118deg,
    rgba(53, 230, 224, 0.16) 0px,
    rgba(53, 230, 224, 0.16) 1px,
    transparent 1px,
    transparent 13px
  );
  mix-blend-mode: screen;
  opacity: 0.5;
}

.media-frame > img {
  position: relative;
  z-index: 1;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

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

/* ---------- 9. 面包屑 ---------- */
.breadcrumb {
  margin-bottom: clamp(18px, 2.4vw, 30px);
}

.breadcrumb ol {
  display: flex;
  flex-wrap: wrap;
  gap: 6px 8px;
  font-size: 13px;
  color: var(--stardust);
}

.breadcrumb a {
  color: var(--stardust);
  text-decoration: none;
  transition: color 0.25s ease;
}

.breadcrumb a:hover { color: var(--neon-cyan); }

.breadcrumb li:not(:last-child)::after {
  content: "／";
  margin-left: 8px;
  color: rgba(154, 163, 192, 0.45);
}

/* ---------- 10. 正文容器 ---------- */
.prose {
  max-width: 68ch;
  font-size: clamp(16px, 0.4vw + 14.4px, 18px);
  line-height: 1.78;
  color: #E9E4D8;
}

.prose h2 {
  margin-top: 2.2em;
  font-size: clamp(22px, 1.8vw + 15px, 30px);
  color: var(--cream);
}

.prose h3 {
  margin-top: 1.7em;
  font-size: clamp(18px, 1vw + 14px, 22px);
  color: var(--neon-cyan);
}

.prose a {
  color: var(--neon-cyan);
  text-decoration: underline;
  text-decoration-thickness: 1px;
  text-underline-offset: 4px;
  transition: color 0.25s ease, text-decoration-color 0.25s ease;
}

.prose a:hover { color: var(--lime); }

.prose ul,
.prose ol {
  margin: 0 0 1.2em;
  padding-left: 1.3em;
}

.prose li { margin-bottom: 0.5em; }
.prose ul li { list-style: none; position: relative; }

.prose ul li::before {
  content: "";
  position: absolute;
  left: -1.05em;
  top: 0.72em;
  width: 7px;
  height: 2px;
  background: var(--neon-cyan);
}

.prose ol { list-style: decimal; }
.prose ol li::marker { color: var(--neon-cyan); font-family: var(--font-mono); font-weight: 700; }

.prose blockquote {
  margin: 1.6em 0;
  padding: 4px 0 4px 20px;
  border-left: 3px solid var(--violet);
  color: var(--stardust);
}

.prose code {
  padding: 0.12em 0.42em;
  border-radius: 5px;
  background: rgba(53, 230, 224, 0.12);
  color: var(--neon-cyan);
  font-family: var(--font-mono);
  font-size: 0.92em;
}

.prose hr {
  margin: 2.4em 0;
  border: 0;
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--line-strong) 30%, var(--line-strong) 70%, transparent);
}

/* =========================================================
   11. 页头：居中刊头
   ========================================================= */
.site-masthead {
  position: sticky;
  top: 0;
  z-index: 100;
  background: linear-gradient(180deg, rgba(11, 16, 38, 0.92) 0%, rgba(11, 16, 38, 0.66) 100%);
  backdrop-filter: blur(18px) saturate(150%);
  -webkit-backdrop-filter: blur(18px) saturate(150%);
}

.masthead-top {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 20px;
  padding-block: 18px 12px;
  transition: padding 0.35s var(--ease);
}

.masthead-brand {
  justify-self: start;
  display: flex;
  flex-direction: column;
  gap: 3px;
  text-decoration: none;
  color: var(--cream);
}

.masthead-brand__name {
  font-family: var(--font-display);
  font-size: clamp(19px, 1.6vw + 13px, 25px);
  font-weight: 800;
  letter-spacing: -0.02em;
  line-height: 1.1;
  transition: color 0.3s ease, text-shadow 0.3s ease;
}

.masthead-brand:hover .masthead-brand__name {
  color: var(--neon-cyan);
  text-shadow: 0 0 22px rgba(53, 230, 224, 0.55);
}

.masthead-brand__sub {
  display: block;
  max-height: 16px;
  overflow: hidden;
  font-family: var(--font-mono);
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 0.34em;
  text-transform: uppercase;
  color: var(--neon-cyan);
  opacity: 0.9;
  transition: opacity 0.3s ease, max-height 0.35s var(--ease);
}

.masthead-tagline {
  margin: 0;
  font-size: 14px;
  font-weight: 500;
  letter-spacing: 0.08em;
  color: var(--stardust);
  text-align: center;
  white-space: nowrap;
  transition: opacity 0.3s ease, transform 0.3s ease;
}

.masthead-actions {
  justify-self: end;
  display: flex;
  align-items: center;
  gap: 10px;
}

/* 移动端栏目按钮 */
.nav-toggle {
  display: none;
  align-items: center;
  gap: 9px;
  padding: 10px 14px;
  border: 1px solid rgba(244, 239, 227, 0.26);
  border-radius: 999px;
  background: rgba(244, 239, 227, 0.05);
  color: var(--cream);
  cursor: pointer;
  transition: border-color 0.3s ease, color 0.3s ease, background-color 0.3s ease;
}

.nav-toggle:hover {
  border-color: var(--neon-cyan);
  color: var(--neon-cyan);
}

.nav-toggle__bars {
  display: grid;
  gap: 4px;
  width: 18px;
}

.nav-toggle__bars i {
  display: block;
  height: 2px;
  border-radius: 2px;
  background: currentColor;
  transition: transform 0.3s var(--ease), opacity 0.25s ease;
}

.nav-toggle__bars i:nth-child(2) { width: 72%; }

.nav-toggle[aria-expanded="true"] .nav-toggle__bars i:nth-child(1) {
  transform: translateY(6px) rotate(45deg);
}
.nav-toggle[aria-expanded="true"] .nav-toggle__bars i:nth-child(2) {
  opacity: 0;
}
.nav-toggle[aria-expanded="true"] .nav-toggle__bars i:nth-child(3) {
  transform: translateY(-6px) rotate(-45deg);
}

.nav-toggle__label {
  font-family: var(--font-display);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.1em;
}

/* 栏目导航 */
.site-nav {
  display: flex;
  justify-content: center;
  padding-bottom: 12px;
  transition: padding 0.35s var(--ease);
}

.site-nav__list {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: clamp(14px, 3vw, 42px);
}

.site-nav__link {
  position: relative;
  display: inline-block;
  padding: 10px 2px 12px;
  font-family: var(--font-display);
  font-size: 15px;
  font-weight: 700;
  letter-spacing: 0.09em;
  color: var(--stardust);
  text-decoration: none;
  transition: color 0.28s ease;
}

.site-nav__link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 6px;
  height: 2px;
  border-radius: 2px;
  background: linear-gradient(90deg, var(--neon-cyan), var(--violet));
  transform: scaleX(0);
  transform-origin: center;
  transition: transform 0.32s var(--ease);
}

.site-nav__link:hover {
  color: var(--cream);
}

.site-nav__link:hover::after { transform: scaleX(1); }

.site-nav__link[aria-current="page"] {
  color: var(--neon-cyan);
  text-shadow: 0 0 20px rgba(53, 230, 224, 0.45);
}

.site-nav__link[aria-current="page"]::after { transform: scaleX(1); }

/* 刊头下缘渐变分隔线 */
.masthead-rule {
  position: relative;
  height: 3px;
  overflow: hidden;
  background: linear-gradient(
    90deg,
    rgba(53, 230, 224, 0) 0%,
    rgba(53, 230, 224, 0.95) 22%,
    var(--violet) 46%,
    var(--aurora-pink) 62%,
    var(--warm-orange) 80%,
    rgba(255, 138, 61, 0) 100%
  );
  opacity: 0.7;
}

.masthead-rule::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(90deg, transparent, rgba(244, 239, 227, 0.9), transparent);
  transform: translateX(-120%);
  animation: rule-sweep 16s linear infinite;
}

@keyframes rule-sweep {
  0%        { transform: translateX(-120%); }
  55%, 100% { transform: translateX(120%); }
}

/* 阅读进度条 */
.scroll-progress {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 2px;
  background: rgba(154, 163, 192, 0.14);
  pointer-events: none;
}

.scroll-progress span {
  display: block;
  width: 0;
  height: 100%;
  background: linear-gradient(90deg, var(--neon-cyan), var(--violet) 60%, var(--warm-orange));
  transition: width 0.12s linear;
}

/* 滚动收窄态 */
.site-masthead[data-scrolled] .masthead-top { padding-block: 9px 5px; }
.site-masthead[data-scrolled] .site-nav { padding-bottom: 6px; }

.site-masthead[data-scrolled] .masthead-brand__sub {
  max-height: 0;
  opacity: 0;
}

.site-masthead[data-scrolled] .masthead-tagline {
  opacity: 0;
  transform: translateY(-5px);
}

/* =========================================================
   12. 页脚
   ========================================================= */
.site-footer {
  position: relative;
  margin-top: clamp(72px, 10vw, 140px);
  background: linear-gradient(180deg, rgba(11, 16, 38, 0.4) 0%, rgba(11, 16, 38, 1) 34%);
  border-top: 1px solid var(--line-cyan);
  color: var(--stardust);
}

/* 草原星空分隔带 */
.footer-band {
  position: relative;
  height: clamp(110px, 15vw, 180px);
  overflow: hidden;
  background:
    radial-gradient(1.5px 1.5px at 11% 24%, rgba(244, 239, 227, 0.95), transparent 62%),
    radial-gradient(1.2px 1.2px at 27% 62%, rgba(53, 230, 224, 0.9), transparent 62%),
    radial-gradient(1.7px 1.7px at 43% 18%, rgba(244, 239, 227, 0.72), transparent 62%),
    radial-gradient(1.1px 1.1px at 58% 48%, rgba(139, 92, 246, 0.95), transparent 62%),
    radial-gradient(1.5px 1.5px at 72% 70%, rgba(244, 239, 227, 0.6), transparent 62%),
    radial-gradient(1.3px 1.3px at 84% 30%, rgba(255, 138, 61, 0.85), transparent 62%),
    radial-gradient(1.1px 1.1px at 94% 58%, rgba(53, 230, 224, 0.7), transparent 62%),
    radial-gradient(1.4px 1.4px at 36% 82%, rgba(255, 111, 181, 0.7), transparent 62%),
    linear-gradient(180deg, rgba(11, 16, 38, 0) 0%, rgba(19, 26, 58, 0.85) 100%);
}

.footer-band::after {
  content: "";
  position: absolute;
  left: -12%;
  right: -12%;
  bottom: -46%;
  height: 78%;
  border-radius: 50% 50% 0 0 / 100% 100% 0 0;
  background: linear-gradient(180deg, rgba(53, 230, 224, 0.2) 0%, rgba(11, 16, 38, 0.96) 82%);
  filter: blur(0.4px);
}

.footer-band::before {
  content: "";
  position: absolute;
  left: 50%;
  bottom: 22px;
  width: 2px;
  height: 34%;
  transform: translateX(-50%);
  background: linear-gradient(180deg, transparent, rgba(53, 230, 224, 0.55), transparent);
  opacity: 0.55;
}

.footer-grid {
  display: grid;
  grid-template-columns: 1.5fr 1fr 1.1fr 1.6fr;
  gap: clamp(24px, 4vw, 56px);
  padding-block: clamp(36px, 5vw, 60px) clamp(26px, 3.5vw, 40px);
}

.footer-col { display: grid; align-content: start; gap: 12px; }

.footer-brand {
  margin: 0;
  font-family: var(--font-display);
  font-size: 22px;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--cream);
}

.footer-slogan {
  margin: 0;
  font-size: 14px;
  line-height: 1.7;
  color: var(--neon-cyan);
  letter-spacing: 0.04em;
}

.footer-title {
  margin: 0 0 4px;
  font-family: var(--font-mono);
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--neon-cyan);
}

.footer-list { display: grid; gap: 9px; }

.footer-list a {
  font-size: 14.5px;
  line-height: 1.6;
  color: var(--stardust);
  text-decoration: none;
  transition: color 0.25s ease, padding-left 0.25s ease;
}

.footer-list a:hover {
  color: var(--cream);
  padding-left: 4px;
}

.footer-list--contact li {
  display: grid;
  gap: 2px;
}

.footer-key {
  font-family: var(--font-mono);
  font-size: 11.5px;
  font-weight: 700;
  letter-spacing: 0.16em;
  color: rgba(154, 163, 192, 0.72);
}

.footer-val {
  font-size: 14.5px;
  line-height: 1.62;
  color: #D8D3C6;
  word-break: break-word;
}

.footer-legal {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 12px 28px;
  padding-block: 20px 40px;
  border-top: 1px solid var(--line);
}

.footer-legal__links {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 22px;
}

.footer-legal__links a {
  font-size: 13.5px;
  color: var(--stardust);
  text-decoration: none;
  transition: color 0.25s ease;
}

.footer-legal__links a:hover { color: var(--neon-cyan); }

.footer-note {
  margin: 0;
  font-family: var(--font-mono);
  font-size: 12.5px;
  letter-spacing: 0.04em;
  color: rgba(154, 163, 192, 0.78);
}

/* =========================================================
   13. 工具层
   ========================================================= */
.skip-link {
  position: fixed;
  top: -64px;
  left: 16px;
  z-index: 220;
  padding: 11px 18px;
  border-radius: 0 0 12px 12px;
  background: var(--neon-cyan);
  color: #04161A;
  font-family: var(--font-display);
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-decoration: none;
  transition: top 0.24s var(--ease);
}

.skip-link:focus { top: 0; }

.back-to-top {
  position: fixed;
  right: clamp(16px, 3vw, 30px);
  bottom: clamp(16px, 3vw, 30px);
  z-index: 90;
  display: grid;
  place-items: center;
  width: 48px;
  height: 48px;
  padding: 0;
  border: 1px solid rgba(53, 230, 224, 0.42);
  border-radius: 50%;
  background: rgba(11, 16, 38, 0.8);
  color: var(--neon-cyan);
  font-size: 17px;
  line-height: 1;
  cursor: pointer;
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  opacity: 0;
  visibility: hidden;
  transform: translateY(12px);
  transition: opacity 0.3s ease, transform 0.3s var(--ease), visibility 0.3s ease, border-color 0.3s ease;
}

.back-to-top[data-visible] {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top:hover { border-color: var(--neon-cyan); }

/* 滚动浮现 */
html.reveal-ready [data-reveal] {
  opacity: 0;
  transform: translateY(16px);
}

html.reveal-ready [data-reveal].is-in {
  opacity: 1;
  transform: none;
  transition: opacity 0.62s var(--ease), transform 0.62s var(--ease);
}

/* 焦点可见 */
:focus-visible {
  outline: 2px solid var(--neon-cyan);
  outline-offset: 3px;
  border-radius: 4px;
}

/* 选中态 */
::selection {
  background: rgba(53, 230, 224, 0.32);
  color: var(--cream);
}

/* =========================================================
   14. 响应式
   ========================================================= */
@media (max-width: 1080px) {
  .footer-grid { grid-template-columns: 1.4fr 1fr 1.2fr; }
  .footer-col--brand { grid-column: 1 / -1; }
}

@media (max-width: 900px) {
  .masthead-top {
    grid-template-columns: 1fr auto auto;
    gap: 10px;
    padding-block: 13px 10px;
  }

  .masthead-tagline { display: none; }

  .masthead-actions .btn--ghost { display: none; }
  .masthead-actions .btn { padding: 10px 14px; font-size: 13px; }

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

  .site-nav {
    display: block;
    max-height: 0;
    padding-bottom: 0;
    overflow: hidden;
    opacity: 0;
    transition: max-height 0.42s var(--ease), opacity 0.28s ease, padding-bottom 0.32s var(--ease);
  }

  .site-nav[data-open] {
    max-height: min(72vh, 540px);
    padding-bottom: 16px;
    overflow-y: auto;
    opacity: 1;
  }

  .site-nav__list {
    flex-direction: column;
    align-items: stretch;
    gap: 0;
  }

  .site-nav__link {
    display: block;
    padding: 13px 4px;
    font-size: 16px;
    border-bottom: 1px solid rgba(154, 163, 192, 0.14);
  }

  .site-nav__link::after { bottom: 0; }

  .grid-3 { grid-template-columns: repeat(2, minmax(0, 1fr)); }

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

  .footer-legal { flex-direction: column; align-items: flex-start; }
}

@media (max-width: 640px) {
  .masthead-brand__sub { letter-spacing: 0.26em; }

  .grid-2,
  .grid-3 { grid-template-columns: minmax(0, 1fr); }

  .footer-grid { grid-template-columns: minmax(0, 1fr); }

  .btn { padding: 11px 16px; font-size: 13.5px; }

  .back-to-top {
    width: 44px;
    height: 44px;
  }
}

/* =========================================================
   15. 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;
  }

  body::before { animation: none; }
  .masthead-rule::after { display: none; }
  .scroll-progress span { transition: none; }

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