/* ============================================================
   博业新站 · 共享样式
   文件：/assets/site.css
   角色：Reset / 变量 / 中文排版 / 头部 / 页脚 / 通用组件
   创意方向：极简文字建筑 · 悬浮玻璃导航 · 控制台状态面板
   ============================================================ */

/* ---------- 设计变量 ---------- */
:root {
  --color-primary: #0A66FF;
  --color-primary-light: #4D94FF;
  --color-primary-dark: #0044CC;
  --color-accent: #FF6B2C;
  --color-accent-light: #FF9E66;
  --color-jewel-teal: #0F766E;
  --color-jewel-wine: #7B1D3B;
  --color-jewel-purple: #6D28D9;
  --color-bg: #F8FAFC;
  --color-bg-glass: rgba(255, 255, 255, 0.72);
  --color-surface: #FFFFFF;
  --color-border: #E2E8F0;
  --color-border-strong: #CBD5E1;
  --color-text: #1E293B;
  --color-text-secondary: #64748B;
  --color-text-muted: #94A3B8;

  --font-family: 'Inter', 'Noto Sans SC', sans-serif;
  --text-xs: 12px;
  --text-sm: 14px;
  --text-base: 16px;
  --text-md: 20px;
  --text-lg: 24px;
  --text-xl: 32px;
  --text-2xl: 40px;
  --text-3xl: 56px;

  --container: 1200px;
  --container-narrow: 760px;
  --header-safe: 104px;
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-pill: 999px;
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 16px;
  --space-lg: 24px;
  --space-xl: 40px;
  --space-2xl: 64px;
  --space-3xl: 96px;
  --ease: cubic-bezier(0.4, 0, 0.2, 1);
  --shadow-sm: 0 1px 3px rgba(30, 41, 59, 0.06);
  --shadow-md: 0 4px 16px rgba(30, 41, 59, 0.08);
  --shadow-lg: 0 12px 32px rgba(30, 41, 59, 0.1);
  --shadow-glass: 0 8px 32px rgba(30, 41, 59, 0.08);
}

/* ---------- Reset ---------- */
*, *::before, *::after {
  box-sizing: border-box;
}
* {
  margin: 0;
  padding: 0;
}
html {
  background-color: var(--color-bg);
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
}
body {
  min-height: 100vh;
  padding-top: var(--header-safe);
  font-family: var(--font-family);
  font-size: var(--text-base);
  font-weight: 400;
  line-height: 1.7;
  letter-spacing: 0.01em;
  color: var(--color-text);
  background-color: var(--color-bg);
  background-image:
    linear-gradient(rgba(148, 163, 184, 0.055) 1px, transparent 1px),
    linear-gradient(90deg, rgba(148, 163, 184, 0.055) 1px, transparent 1px);
  background-size: 32px 32px;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}
h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.15;
  color: inherit;
}
p {
  margin-bottom: 1em;
}
a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color 0.2s var(--ease);
}
a:hover {
  color: var(--color-primary-dark);
}
ul, ol {
  list-style: none;
}
img, svg, video {
  display: block;
  max-width: 100%;
  height: auto;
}
button, input, select, textarea {
  font: inherit;
  color: inherit;
}
::selection {
  background: rgba(10, 102, 255, 0.16);
  color: var(--color-text);
}

/* ---------- 排版体系 ---------- */
.h-display {
  font-size: clamp(34px, 5vw, var(--text-3xl));
  font-weight: 700;
  letter-spacing: -0.03em;
  line-height: 1.05;
  color: var(--color-text);
}
.h1 {
  font-size: var(--text-2xl);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.15;
}
.h2 {
  font-size: var(--text-xl);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.2;
}
.h3 {
  font-size: var(--text-lg);
  font-weight: 700;
  letter-spacing: -0.01em;
  line-height: 1.25;
}
.h4 {
  font-size: var(--text-md);
  font-weight: 700;
  line-height: 1.3;
}
.lead {
  font-size: var(--text-md);
  line-height: 1.65;
  color: var(--color-text-secondary);
  max-width: 60ch;
}
.text-secondary {
  color: var(--color-text-secondary);
}
.text-accent {
  color: var(--color-accent);
}
.text-center {
  text-align: center;
}

/* ---------- 布局与容器 ---------- */
.container {
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 24px;
}
.container-narrow {
  max-width: var(--container-narrow);
  margin: 0 auto;
  padding: 0 24px;
}
.section {
  padding: var(--space-2xl) 0;
}
.section-sm {
  padding: var(--space-xl) 0;
}
.site-main {
  width: 100%;
}
#main-content {
  scroll-margin-top: calc(var(--header-safe) + 16px);
}

/* ---------- 短眉标 / 编号章节 ---------- */
.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: var(--text-xs);
  font-weight: 700;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--color-primary);
}
.eyebrow::before {
  content: "";
  width: 16px;
  height: 2px;
  border-radius: 2px;
  background: var(--color-primary);
}
.chapter {
  padding: var(--space-2xl) 0;
}
.chapter-header {
  display: flex;
  align-items: baseline;
  gap: 18px;
  margin-bottom: var(--space-lg);
}
.chapter-num {
  font-size: var(--text-3xl);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1;
  color: var(--color-primary);
  font-variant-numeric: tabular-nums;
}
.chapter-title {
  font-size: var(--text-lg);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.2;
}
.chapter-lead {
  max-width: 60ch;
  color: var(--color-text-secondary);
  font-size: var(--text-base);
  line-height: 1.7;
}

/* ---------- 栅格与卡片 ---------- */
.grid {
  display: grid;
  gap: var(--space-lg);
}
.grid-2 {
  grid-template-columns: repeat(2, 1fr);
}
.grid-3 {
  grid-template-columns: repeat(3, 1fr);
}
.grid-4 {
  grid-template-columns: repeat(4, 1fr);
}
@media (max-width: 960px) {
  .grid-3,
  .grid-4 {
    grid-template-columns: repeat(2, 1fr);
  }
}
@media (max-width: 640px) {
  .grid-2,
  .grid-3,
  .grid-4 {
    grid-template-columns: 1fr;
  }
}
.card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-lg);
  transition: border-color 0.2s var(--ease), box-shadow 0.2s var(--ease), transform 0.2s var(--ease);
}
.card:hover {
  border-color: rgba(10, 102, 255, 0.35);
  box-shadow: var(--shadow-md);
  transform: translateY(-4px);
}
.card-title {
  margin-bottom: 8px;
  font-size: var(--text-md);
  font-weight: 700;
  letter-spacing: -0.01em;
}
.card-text {
  color: var(--color-text-secondary);
  font-size: var(--text-sm);
  margin: 0;
}

/* ---------- 玻璃 / 状态 ---------- */
.glass-panel {
  background: var(--color-bg-glass);
  -webkit-backdrop-filter: blur(14px);
  backdrop-filter: blur(14px);
  border: 1px solid rgba(255, 255, 255, 0.65);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
}
.status-bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 12px 24px;
  padding: 14px 18px;
  background: var(--color-bg-glass);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: var(--text-sm);
  color: var(--color-text-secondary);
}
.status-dot {
  display: inline-block;
  flex: none;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--color-border-strong);
}
.status-dot-online {
  background: var(--color-accent);
  box-shadow: 0 0 0 3px rgba(255, 107, 44, 0.18);
}

/* ---------- 按钮 ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 24px;
  border: 1px solid transparent;
  border-radius: var(--radius-pill);
  font-size: var(--text-sm);
  font-weight: 600;
  line-height: 1.4;
  cursor: pointer;
  transition: background-color 0.2s var(--ease), color 0.2s var(--ease), border-color 0.2s var(--ease), box-shadow 0.2s var(--ease);
}
.btn-primary {
  background: var(--color-primary);
  color: #fff;
}
.btn-primary:hover {
  background: var(--color-primary-dark);
  color: #fff;
  box-shadow: 0 4px 16px rgba(10, 102, 255, 0.3);
}
.btn-accent {
  background: var(--color-accent);
  color: #fff;
}
.btn-accent:hover {
  background: var(--color-accent-light);
  color: #fff;
  box-shadow: 0 4px 16px rgba(255, 107, 44, 0.3);
}
.btn-ghost {
  background: transparent;
  border-color: var(--color-border-strong);
  color: var(--color-text);
}
.btn-ghost:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
}
.btn-lg {
  padding: 16px 32px;
  font-size: var(--text-base);
}

/* ---------- 面包屑（浏览路径） ---------- */
.breadcrumb {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 6px;
  padding: 20px 0;
  font-size: var(--text-sm);
  color: var(--color-text-secondary);
}
.breadcrumb-list {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 6px;
}
.breadcrumb-item a {
  color: var(--color-text-secondary);
  transition: color 0.2s var(--ease);
}
.breadcrumb-item a:hover {
  color: var(--color-primary);
}
.breadcrumb-item[aria-current="page"] {
  color: var(--color-text);
  font-weight: 600;
}
.breadcrumb-sep {
  color: var(--color-border-strong);
  user-select: none;
}

/* ---------- 图片容器 ---------- */
.media-frame {
  position: relative;
  overflow: hidden;
  aspect-ratio: 16 / 9;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  background: linear-gradient(135deg, var(--color-border) 0%, #F1F5F9 100%);
}
.media-frame img,
.media-frame video {
  width: 100%;
  height: 100%;
  object-fit: cover;
}
.media-frame[data-label]::after {
  content: attr(data-label);
  position: absolute;
  left: 12px;
  bottom: 12px;
  padding: 5px 12px;
  border-radius: var(--radius-pill);
  background: rgba(15, 23, 42, 0.72);
  color: #fff;
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.02em;
}
.media-frame-ratio-4-3 {
  aspect-ratio: 4 / 3;
}
.media-frame-ratio-1-1 {
  aspect-ratio: 1 / 1;
}
.media-frame-ratio-vertical {
  aspect-ratio: 3 / 4;
}

/* ---------- 跳转链接 ---------- */
.skip-link {
  position: fixed;
  top: 12px;
  left: 12px;
  z-index: 500;
  display: inline-flex;
  align-items: center;
  padding: 10px 20px;
  border-radius: var(--radius-pill);
  background: var(--color-primary);
  color: #fff;
  font-size: var(--text-sm);
  font-weight: 600;
  line-height: 1;
  box-shadow: var(--shadow-md);
  opacity: 0;
  pointer-events: none;
  transform: translateY(-160%);
  transition: transform 0.25s var(--ease), opacity 0.25s var(--ease);
}
.skip-link:focus-visible {
  opacity: 1;
  pointer-events: auto;
  transform: translateY(0);
  outline: none;
  box-shadow: var(--shadow-md), 0 0 0 3px var(--color-primary-light);
}

/* ---------- 头部与悬浮胶囊导航 ---------- */
.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  padding: 16px 20px 0;
  pointer-events: none;
}
.nav-capsule {
  max-width: var(--container);
  margin: 0 auto;
  display: flex;
  align-items: center;
  gap: var(--space-md);
  padding: 8px 10px 8px 14px;
  background: var(--color-bg-glass);
  -webkit-backdrop-filter: blur(14px);
  backdrop-filter: blur(14px);
  border: 1px solid rgba(255, 255, 255, 0.65);
  border-radius: var(--radius-pill);
  box-shadow: var(--shadow-glass);
  pointer-events: auto;
}
.nav-brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 4px 8px 4px 4px;
  border-radius: var(--radius-pill);
  color: var(--color-text);
  transition: background-color 0.2s var(--ease);
}
.nav-brand:hover {
  background: rgba(10, 102, 255, 0.06);
  color: var(--color-text);
}
.brand-mark {
  position: relative;
  flex: none;
  width: 32px;
  height: 32px;
  border-radius: 10px;
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-jewel-purple) 100%);
  box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.2);
  overflow: hidden;
}
.brand-mark::before {
  content: "";
  position: absolute;
  top: 6px;
  left: 6px;
  width: 12px;
  height: 12px;
  border-radius: 4px;
  background: var(--color-accent);
}
.brand-mark::after {
  content: "";
  position: absolute;
  right: 5px;
  bottom: 5px;
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: #fff;
  opacity: 0.9;
}
.brand-name {
  font-size: var(--text-md);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1;
}
.brand-desc {
  display: none;
  margin-left: 2px;
  padding-left: 14px;
  border-left: 1px solid var(--color-border-strong);
  font-size: var(--text-xs);
  font-weight: 400;
  letter-spacing: 0.02em;
  color: var(--color-text-secondary);
  white-space: nowrap;
}
@media (min-width: 1180px) {
  .brand-desc {
    display: inline-block;
  }
}
.nav-capsule-links {
  display: flex;
  align-items: center;
  gap: 2px;
  margin-left: auto;
}
.nav-link {
  display: inline-flex;
  align-items: center;
  padding: 8px 14px;
  border-radius: var(--radius-pill);
  color: var(--color-text);
  font-size: var(--text-sm);
  font-weight: 600;
  letter-spacing: 0.01em;
  line-height: 1.2;
  white-space: nowrap;
  transition: background-color 0.2s var(--ease), color 0.2s var(--ease), box-shadow 0.2s var(--ease);
}
.nav-link:hover {
  background: rgba(10, 102, 255, 0.07);
  color: var(--color-primary);
}
.nav-link[aria-current="page"] {
  background: var(--color-primary);
  color: #fff;
  box-shadow: 0 2px 8px rgba(10, 102, 255, 0.28);
}
.nav-cta {
  margin-left: 6px;
  background: rgba(255, 107, 44, 0.1);
  color: var(--color-accent);
}
.nav-cta:hover {
  background: var(--color-accent);
  color: #fff;
  box-shadow: 0 4px 12px rgba(255, 107, 44, 0.3);
}
.nav-cta[aria-current="page"] {
  background: var(--color-accent);
  color: #fff;
  box-shadow: 0 2px 8px rgba(255, 107, 44, 0.3);
}

/* ---------- 移动端开关与面板 ---------- */
.nav-toggle {
  display: none;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 5px;
  width: 40px;
  height: 40px;
  margin-left: auto;
  padding: 0;
  border: 1px solid var(--color-border);
  border-radius: 50%;
  background: transparent;
  cursor: pointer;
  transition: border-color 0.2s var(--ease), background-color 0.2s var(--ease);
}
.nav-toggle:hover {
  border-color: var(--color-primary);
  background: rgba(10, 102, 255, 0.06);
}
.nav-toggle[aria-expanded="true"] {
  border-color: var(--color-primary);
  background: rgba(10, 102, 255, 0.08);
}
.nav-toggle-line {
  display: block;
  width: 18px;
  height: 2px;
  border-radius: 2px;
  background: var(--color-text);
  transition: transform 0.25s var(--ease), opacity 0.2s var(--ease), background-color 0.2s var(--ease);
}
.nav-toggle[aria-expanded="true"] .nav-toggle-line {
  background: var(--color-primary);
}
.nav-toggle[aria-expanded="true"] .nav-toggle-line:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}
.nav-toggle[aria-expanded="true"] .nav-toggle-line:nth-child(2) {
  opacity: 0;
}
.nav-toggle[aria-expanded="true"] .nav-toggle-line:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}
.nav-mobile {
  display: none;
  max-width: calc(var(--container) - 40px);
  margin: 8px auto 0;
  padding: 8px;
  background: var(--color-bg-glass);
  -webkit-backdrop-filter: blur(16px);
  backdrop-filter: blur(16px);
  border: 1px solid rgba(255, 255, 255, 0.65);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  pointer-events: auto;
}
.nav-mobile[data-open] {
  display: block;
}
.nav-mobile-links {
  display: flex;
  flex-direction: column;
  gap: 2px;
}
.nav-mobile-link {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 18px;
  border-radius: var(--radius-md);
  color: var(--color-text);
  font-size: var(--text-base);
  font-weight: 600;
  line-height: 1.3;
  transition: background-color 0.2s var(--ease), color 0.2s var(--ease);
}
.nav-mobile-link:hover {
  background: rgba(10, 102, 255, 0.07);
  color: var(--color-primary);
}
.nav-mobile-link[aria-current="page"] {
  background: rgba(10, 102, 255, 0.08);
  color: var(--color-primary);
  font-weight: 700;
}
.nav-mobile-label {
  display: inline-block;
}
.nav-mobile-index {
  font-size: var(--text-xs);
  font-weight: 700;
  letter-spacing: 0.04em;
  color: var(--color-text-muted);
  font-variant-numeric: tabular-nums;
}
.nav-mobile-cta {
  color: var(--color-accent);
}
.nav-mobile-cta .nav-mobile-index {
  color: var(--color-accent);
}
.nav-mobile-cta[aria-current="page"] {
  background: rgba(255, 107, 44, 0.1);
  color: var(--color-accent);
}
@media (max-width: 960px) {
  .nav-capsule-links {
    display: none;
  }
  .nav-toggle {
    display: inline-flex;
  }
}

/* ---------- 页脚 · 控制台状态台 ---------- */
.site-footer {
  position: relative;
  margin-top: var(--space-3xl);
  padding: 64px 24px 28px;
  background:
    radial-gradient(560px 280px at 88% -10%, rgba(109, 40, 217, 0.32), transparent 70%),
    radial-gradient(480px 260px at 6% 115%, rgba(15, 118, 110, 0.28), transparent 70%),
    radial-gradient(360px 200px at 40% 0%, rgba(123, 29, 59, 0.16), transparent 70%),
    linear-gradient(135deg, #0B1220 0%, #111C2E 50%, #0E1A38 100%);
  color: #E2E8F0;
  border-radius: 32px 32px 0 0;
  overflow: hidden;
}
.site-footer::before {
  content: "";
  position: absolute;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  width: min(720px, 80vw);
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--color-primary-light), transparent);
}
.footer-status {
  position: relative;
  max-width: var(--container);
  margin: 0 auto 48px;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 12px 28px;
  padding-bottom: 28px;
  border-bottom: 1px solid rgba(226, 232, 240, 0.12);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--color-text-muted);
}
.footer-status-item {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-weight: 500;
}
.footer-main {
  position: relative;
  max-width: var(--container);
  margin: 0 auto;
  display: grid;
  grid-template-columns: 1.8fr 1fr 1fr 1.4fr;
  gap: 40px;
}
@media (max-width: 960px) {
  .footer-main {
    grid-template-columns: 1fr 1fr;
    gap: 32px;
  }
}
@media (max-width: 640px) {
  .footer-main {
    grid-template-columns: 1fr;
    gap: 32px;
  }
}
.footer-brand-col {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
}
.footer-brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: #F8FAFC;
  font-size: var(--text-md);
  font-weight: 700;
  letter-spacing: -0.02em;
  transition: opacity 0.2s var(--ease);
}
.footer-brand:hover {
  color: #fff;
  opacity: 0.9;
}
.footer-tagline {
  max-width: 28ch;
  margin: 18px 0 12px;
  font-size: var(--text-base);
  font-weight: 600;
  letter-spacing: 0;
  line-height: 1.5;
  color: #E2E8F0;
}
.footer-trust {
  max-width: 34ch;
  margin: 0;
  font-size: var(--text-xs);
  line-height: 1.65;
  color: #94A3B8;
}
.footer-nav {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 12px;
}
.footer-title {
  margin-bottom: 4px;
  font-size: var(--text-sm);
  font-weight: 700;
  letter-spacing: 0.06em;
  color: #F8FAFC;
}
.footer-link {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: #94A3B8;
  font-size: var(--text-sm);
  font-weight: 500;
  letter-spacing: 0.02em;
  transition: color 0.2s var(--ease), transform 0.2s var(--ease);
}
.footer-link::before {
  content: "";
  flex: none;
  width: 5px;
  height: 5px;
  border-radius: 1px;
  background: rgba(148, 163, 184, 0.5);
  transition: background-color 0.2s var(--ease);
}
.footer-link:hover {
  color: var(--color-primary-light);
  transform: translateX(3px);
}
.footer-link:hover::before {
  background: var(--color-primary-light);
}
.footer-contact-col {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
}
.footer-contact-item {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 5px 0;
  color: #94A3B8;
  font-size: var(--text-sm);
  font-weight: 500;
  line-height: 1.6;
  letter-spacing: 0.02em;
}
.footer-contact-item::before {
  content: "";
  flex: none;
  width: 6px;
  height: 6px;
  margin-top: 8px;
  border-radius: 1px;
  background: var(--color-primary-light);
}
.footer-contact-email {
  font-variant-numeric: tabular-nums;
}
.footer-contact-phone::before {
  background: var(--color-accent);
}
.footer-contact-address::before {
  background: var(--color-jewel-teal);
}
.footer-bottom {
  position: relative;
  max-width: var(--container);
  margin: 48px auto 0;
  padding-top: 22px;
  border-top: 1px solid rgba(226, 232, 240, 0.1);
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 8px 24px;
  font-size: var(--text-xs);
  letter-spacing: 0.02em;
  color: #94A3B8;
}

/* ---------- 滚动进度与返回顶部 ---------- */
.scroll-progress {
  position: fixed;
  top: 0;
  left: 0;
  z-index: 600;
  width: 0%;
  height: 3px;
  border-radius: 0 3px 3px 0;
  background: linear-gradient(90deg, var(--color-primary) 0%, var(--color-jewel-purple) 60%, var(--color-accent) 100%);
  pointer-events: none;
}
.back-to-top {
  position: fixed;
  right: 24px;
  bottom: 24px;
  z-index: 200;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 46px;
  height: 46px;
  border: 1px solid var(--color-border);
  border-radius: 50%;
  background: var(--color-bg-glass);
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
  color: var(--color-text);
  box-shadow: var(--shadow-md);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(10px);
  transition: opacity 0.25s var(--ease), visibility 0.25s, transform 0.25s var(--ease), border-color 0.2s var(--ease), color 0.2s var(--ease);
}
.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}
.back-to-top:hover {
  border-color: var(--color-primary);
  color: var(--color-primary);
  box-shadow: var(--shadow-lg);
}
.back-to-top::before {
  content: "";
  width: 8px;
  height: 8px;
  border-style: solid;
  border-color: currentColor;
  border-width: 2px 2px 0 0;
  transform: rotate(-45deg);
}

/* ---------- 焦点与动效偏好 ---------- */
:focus-visible {
  outline: 3px solid var(--color-primary-light);
  outline-offset: 2px;
  border-radius: 6px;
}
@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    transition-delay: 0s !important;
  }
  .card:hover,
  .footer-link:hover,
  .back-to-top {
    transform: none;
  }
}