:root {
  --color-primary: #1a3a5c;
  --color-primary-light: #2e6f9e;
  --color-accent: #4a9fd4;
  --color-accent-2: #3b86b5;
  --color-bg: #f5f8fb;
  --color-bg-alt: #eaf1f7;
  --color-surface: #ffffff;
  --color-surface-glass: rgba(255, 255, 255, 0.72);
  --color-border: rgba(26, 58, 92, 0.12);
  --color-text: #1c2b3a;
  --color-text-soft: #4a5a6b;
  --color-text-muted: #6b7c8d;
  --color-link: #1f5f8b;
  --color-link-hover: #2e6f9e;
  --color-shadow: rgba(26, 58, 92, 0.12);
  --color-shadow-strong: rgba(26, 58, 92, 0.22);
  --gradient-banner: linear-gradient(135deg, #1a3a5c 0%, #2e6f9e 45%, #4a9fd4 100%);
  --gradient-soft: linear-gradient(135deg, #eaf1f7 0%, #d8e6f2 100%);
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 22px;
  --radius-xl: 32px;
  --radius-pill: 999px;
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 24px;
  --space-6: 32px;
  --space-7: 48px;
  --space-8: 64px;
  --space-9: 96px;
  --font-sans: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans SC", "Helvetica Neue", Arial, sans-serif;
  --font-mono: "SFMono-Regular", "JetBrains Mono", Consolas, monospace;
  --transition-fast: 160ms ease;
  --transition-base: 260ms cubic-bezier(0.22, 0.61, 0.36, 1);
  --transition-slow: 480ms cubic-bezier(0.22, 0.61, 0.36, 1);
  --max-width: 1200px;
  --header-height: 72px;
  color-scheme: light;
}

[data-theme="dark"],
html.dark,
body.dark {
  --color-primary: #0f2236;
  --color-primary-light: #1c4a72;
  --color-accent: #5fb2e6;
  --color-accent-2: #4a9fd4;
  --color-bg: #0b1622;
  --color-bg-alt: #0f1e2d;
  --color-surface: #132436;
  --color-surface-glass: rgba(19, 36, 54, 0.72);
  --color-border: rgba(120, 170, 210, 0.16);
  --color-text: #e6eef6;
  --color-text-soft: #b6c6d6;
  --color-text-muted: #8ba0b4;
  --color-link: #7cc4f0;
  --color-link-hover: #a5d8f7;
  --color-shadow: rgba(0, 0, 0, 0.4);
  --color-shadow-strong: rgba(0, 0, 0, 0.6);
  --gradient-banner: linear-gradient(135deg, #0b1a2a 0%, #123a5c 50%, #1f5f8b 100%);
  --gradient-soft: linear-gradient(135deg, #0f1e2d 0%, #132436 100%);
  color-scheme: dark;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --color-primary: #0f2236;
    --color-primary-light: #1c4a72;
    --color-accent: #5fb2e6;
    --color-accent-2: #4a9fd4;
    --color-bg: #0b1622;
    --color-bg-alt: #0f1e2d;
    --color-surface: #132436;
    --color-surface-glass: rgba(19, 36, 54, 0.72);
    --color-border: rgba(120, 170, 210, 0.16);
    --color-text: #e6eef6;
    --color-text-soft: #b6c6d6;
    --color-text-muted: #8ba0b4;
    --color-link: #7cc4f0;
    --color-link-hover: #a5d8f7;
    --color-shadow: rgba(0, 0, 0, 0.4);
    --color-shadow-strong: rgba(0, 0, 0, 0.6);
    --gradient-banner: linear-gradient(135deg, #0b1a2a 0%, #123a5c 50%, #1f5f8b 100%);
    --gradient-soft: linear-gradient(135deg, #0f1e2d 0%, #132436 100%);
    color-scheme: dark;
  }
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-height) + var(--space-4));
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.75;
  color: var(--color-text);
  background-color: var(--color-bg);
  background-image:
    radial-gradient(1200px 600px at 10% -10%, rgba(74, 159, 212, 0.10), transparent 60%),
    radial-gradient(1000px 500px at 100% 0%, rgba(46, 111, 158, 0.08), transparent 55%);
  background-attachment: fixed;
  transition: background-color var(--transition-base), color var(--transition-base);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

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

a {
  color: var(--color-link);
  text-decoration: none;
  transition: color var(--transition-fast), opacity var(--transition-fast);
}

a:hover,
a:focus-visible {
  color: var(--color-link-hover);
  text-decoration: underline;
  text-underline-offset: 3px;
}

a:focus-visible,
button:focus-visible,
input:focus-visible,
summary:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 3px;
  border-radius: var(--radius-sm);
}

h1, h2, h3, h4, h5, h6 {
  margin: 0 0 var(--space-4);
  line-height: 1.3;
  font-weight: 700;
  color: var(--color-text);
  letter-spacing: -0.01em;
}

h1 {
  font-size: clamp(1.75rem, 1.2rem + 2.4vw, 2.75rem);
  font-weight: 800;
  letter-spacing: -0.02em;
}

h2 {
  font-size: clamp(1.4rem, 1.1rem + 1.4vw, 2rem);
  position: relative;
  padding-bottom: var(--space-3);
}

h2::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: 0;
  width: 56px;
  height: 4px;
  border-radius: var(--radius-pill);
  background: linear-gradient(90deg, var(--color-accent), var(--color-accent-2));
}

h3 {
  font-size: clamp(1.1rem, 1rem + 0.5vw, 1.3rem);
  color: var(--color-primary-light);
}

[data-theme="dark"] h3,
html.dark h3,
body.dark h3 {
  color: var(--color-accent);
}

p {
  margin: 0 0 var(--space-4);
  color: var(--color-text-soft);
}

ul, ol {
  margin: 0 0 var(--space-4);
  padding-left: 1.4em;
  color: var(--color-text-soft);
}

li {
  margin-bottom: var(--space-2);
}

li::marker {
  color: var(--color-accent);
}

blockquote {
  margin: var(--space-5) 0;
  padding: var(--space-4) var(--space-5);
  border-left: 4px solid var(--color-accent);
  border-radius: var(--radius-md);
  background: var(--color-surface-glass);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  box-shadow: 0 6px 20px var(--color-shadow);
  font-style: normal;
}

blockquote p {
  margin: 0;
  color: var(--color-text);
}

strong {
  color: var(--color-text);
  font-weight: 700;
}

address {
  font-style: normal;
}

hr {
  border: 0;
  height: 1px;
  background: var(--color-border);
  margin: var(--space-6) 0;
}

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

a[href="#main-content"] {
  position: absolute;
  top: -100px;
  left: var(--space-4);
  z-index: 999;
  padding: var(--space-3) var(--space-5);
  border-radius: var(--radius-pill);
  background: var(--color-primary);
  color: #fff;
  font-weight: 600;
  box-shadow: 0 8px 24px var(--color-shadow-strong);
  transition: top var(--transition-base);
}

a[href="#main-content"]:focus {
  top: var(--space-3);
  color: #fff;
  text-decoration: none;
}

header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--color-surface-glass);
  backdrop-filter: blur(18px) saturate(160%);
  -webkit-backdrop-filter: blur(18px) saturate(160%);
  border-bottom: 1px solid var(--color-border);
  box-shadow: 0 4px 24px var(--color-shadow);
  transition: background-color var(--transition-base), box-shadow var(--transition-base);
}

header > div {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: var(--space-3) var(--space-5);
  display: flex;
  align-items: center;
  gap: var(--space-4);
  flex-wrap: wrap;
  min-height: var(--header-height);
}

header > div > a[aria-label="中国X站首页"] {
  font-size: 1.25rem;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--color-text);
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-md);
  background: linear-gradient(135deg, var(--color-primary), var(--color-primary-light));
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  transition: transform var(--transition-base), filter var(--transition-base);
  flex-shrink: 0;
}

header > div > a[aria-label="中国X站首页"]:hover {
  text-decoration: none;
  transform: translateY(-1px);
  filter: brightness(1.15);
}

header nav {
  flex: 1 1 auto;
  min-width: 0;
}

header nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-1);
  align-items: center;
}

header nav li {
  margin: 0;
}

header nav a {
  display: inline-block;
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-pill);
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--color-text-soft);
  transition: background-color var(--transition-fast), color var(--transition-fast), transform var(--transition-fast);
  white-space: nowrap;
}

header nav a:hover,
header nav a:focus-visible {
  color: var(--color-primary);
  background: rgba(74, 159, 212, 0.14);
  text-decoration: none;
  transform: translateY(-1px);
}

[data-theme="dark"] header nav a:hover,
html.dark header nav a:hover,
body.dark header nav a:hover {
  color: var(--color-accent);
}

header form[role="search"] {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  flex: 0 1 320px;
  min-width: 200px;
}

header form[role="search"] label {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

header form[role="search"] input[type="search"] {
  flex: 1 1 auto;
  min-width: 0;
  padding: var(--space-2) var(--space-4);
  font-size: 0.9rem;
  font-family: inherit;
  color: var(--color-text);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast), background-color var(--transition-fast);
}

header form[role="search"] input[type="search"]::placeholder {
  color: var(--color-text-muted);
}

header form[role="search"] input[type="search"]:focus {
  outline: none;
  border-color: var(--color-accent);
  box-shadow: 0 0 0 4px rgba(74, 159, 212, 0.18);
}

header form[role="search"] button {
  flex: 0 0 auto;
  padding: var(--space-2) var(--space-4);
  font-size: 0.9rem;
  font-weight: 600;
  font-family: inherit;
  color: #fff;
  background: linear-gradient(135deg, var(--color-primary-light), var(--color-accent));
  border: none;
  border-radius: var(--radius-pill);
  cursor: pointer;
  transition: transform var(--transition-fast), box-shadow var(--transition-fast), filter var(--transition-fast);
  box-shadow: 0 4px 14px rgba(46, 111, 158, 0.32);
}

header form[role="search"] button:hover {
  transform: translateY(-1px);
  filter: brightness(1.08);
  box-shadow: 0 8px 20px rgba(46, 111, 158, 0.42);
}

header form[role="search"] button:active {
  transform: translateY(0);
}

#theme-toggle,
#menu-toggle {
  flex: 0 0 auto;
  padding: var(--space-2) var(--space-4);
  font-size: 0.85rem;
  font-weight: 600;
  font-family: inherit;
  color: var(--color-text);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  cursor: pointer;
  transition: background-color var(--transition-fast), color var(--transition-fast), transform var(--transition-fast), box-shadow var(--transition-fast);
}

#theme-toggle:hover,
#menu-toggle:hover {
  background: var(--color-bg-alt);
  transform: translateY(-1px);
  box-shadow: 0 4px 14px var(--color-shadow);
}

#menu-toggle {
  display: none;
}

main {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: var(--space-6) var(--space-5) var(--space-8);
  display: flex;
  flex-direction: column;
  gap: var(--space-7);
}

main > section {
  position: relative;
  scroll-margin-top: calc(var(--header-height) + var(--space-4));
}

#hero {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: var(--space-7);
  align-items: center;
  padding: var(--space-8) var(--space-7);
  border-radius: var(--radius-xl);
  background: var(--gradient-banner);
  color: #fff;
  box-shadow: 0 24px 60px -20px rgba(26, 58, 92, 0.55);
  overflow: hidden;
  isolation: isolate;
}

#hero::before {
  content: "";
  position: absolute;
  inset: 0;
  z-index: -1;
  background:
    radial-gradient(600px 300px at 85% 15%, rgba(255, 255, 255, 0.18), transparent 60%),
    radial-gradient(500px 260px at 10% 90%, rgba(74, 159, 212, 0.35), transparent 65%);
  pointer-events: none;
}

#hero::after {
  content: "";
  position: absolute;
  top: -40%;
  right: -10%;
  width: 420px;
  height: 420px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(255, 255, 255, 0.14), transparent 70%);
  z-index: -1;
  pointer-events: none;
}

#hero h1 {
  color: #fff;
  text-shadow: 0 2px 20px rgba(0, 0, 0, 0.25);
}

#hero p {
  color: rgba(255, 255, 255, 0.88);
  font-size: 1.02rem;
}

#hero p:last-child {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  margin-top: var(--space-5);
}

#hero p:last-child a {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: var(--space-3) var(--space-6);
  font-weight: 700;
  font-size: 0.95rem;
  border-radius: var(--radius-pill);
  transition: transform var(--transition-base), box-shadow var(--transition-base), background-color var(--transition-fast), color var(--transition-fast);
  text-decoration: none;
}

#hero p:last-child a:first-child {
  color: var(--color-primary);
  background: #fff;
  box-shadow: 0 10px 26px rgba(0, 0, 0, 0.22);
}

#hero p:last-child a:first-child:hover {
  transform: translateY(-2px);
  box-shadow: 0 16px 34px rgba(0, 0, 0, 0.3);
  color: var(--color-primary);
}

#hero p:last-child a:last-child {
  color: #fff;
  background: rgba(255, 255, 255, 0.14);
  border: 1px solid rgba(255, 255, 255, 0.4);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
}

#hero p:last-child a:last-child:hover {
  background: rgba(255, 255, 255, 0.24);
  transform: translateY(-2px);
  color: #fff;
}

#hero figure {
  margin: 0;
  border-radius: var(--radius-lg);
  overflow: hidden;
  background: rgba(255, 255, 255, 0.08);
  border: 1px solid rgba(255, 255, 255, 0.18);
  padding: var(--space-3);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  box-shadow: 0 20px 50px -12px rgba(0, 0, 0, 0.45);
  transition: transform var(--transition-slow), box-shadow var(--transition-slow);
}

#hero figure:hover {
  transform: translateY(-6px) scale(1.01);
  box-shadow: 0 30px 70px -14px rgba(0, 0, 0, 0.55);
}

#hero figure svg {
  border-radius: var(--radius-md);
  width: 100%;
  height: auto;
}

#hero figcaption {
  margin-top: var(--space-3);
  font-size: 0.82rem;
  color: rgba(255, 255, 255, 0.72);
  text-align: center;
}

#about,
#products,
#solutions,
#cases,
#news,
#articles,
#howto,
#faq,
#contact,
#sitemap,
#links {
  padding: var(--space-7) var(--space-6);
  border-radius: var(--radius-xl);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  box-shadow: 0 12px 40px -18px var(--color-shadow-strong);
  transition: box-shadow var(--transition-slow), transform var(--transition-slow), background-color var(--transition-base), border-color var(--transition-base);
}

#about:hover,
#products:hover,
#solutions:hover,
#cases:hover,
#news:hover,
#articles:hover,
#howto:hover,
#faq:hover,
#contact:hover,
#sitemap:hover,
#links:hover {
  box-shadow: 0 20px 56px -20px var(--color-shadow-strong);
}

#products,
#articles {
  background: var(--gradient-soft);
}

#faq {
  background: var(--color-surface-glass);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
}

#news article,
#articles article {
  padding: var(--space-5);
  margin-bottom: var(--space-4);
  border-radius: var(--radius-lg);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  box-shadow: 0 6px 20px -10px var(--color-shadow);
  transition: transform var(--transition-base), box-shadow var(--transition-base), border-color var(--transition-base);
}

#news article:hover,
#articles article:hover {
  transform: translateY(-4px);
  box-shadow: 0 18px 40px -16px var(--color-shadow-strong);
  border-color: rgba(74, 159, 212, 0.4);
}

#news article:last-child,
#articles article:last-child {
  margin-bottom: 0;
}

#news article h3,
#articles article h3 {
  margin-bottom: var(--space-2);
}

#news article p,
#articles article p {
  margin-bottom: var(--space-2);
  font-size: 0.95rem;
}

#news article p:first-of-type,
#articles article p:first-of-type {
  font-size: 0.82rem;
  color: var(--color-text-muted);
  font-family: var(--font-mono);
  letter-spacing: 0.01em;
}

#news article a,
#articles article a {
  display: inline-block;
  font-weight: 600;
  font-size: 0.9rem;
  padding: var(--space-1) 0;
  position: relative;
}

#news article a::after,
#articles article a::after {
  content: "→";
  margin-left: var(--space-1);
  transition: transform var(--transition-fast);
  display: inline-block;
}

#news article a:hover::after,
#articles article a:hover::after {
  transform: translateX(4px);
}

#howto ol {
  counter-reset: howto;
  list-style: none;
  padding-left: 0;
}

#howto ol li {
  counter-increment: howto;
  position: relative;
  padding: var(--space-3) var(--space-4) var(--space-3) var(--space-8);
  margin-bottom: var(--space-3);
  border-radius: var(--radius-md);
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

#howto ol li::before {
  content: counter(howto);
  position: absolute;
  left: var(--space-3);
  top: 50%;
  transform: translateY(-50%);
  width: 28px;
  height: 28px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--color-primary-light), var(--color-accent));
  color: #fff;
  font-weight: 700;
  font-size: 0.85rem;
}

#howto ol li:hover {
  transform: translateX(4px);
  box-shadow: 0 6px 18px -8px var(--color-shadow-strong);
}

#faq details {
  margin-bottom: var(--space-3);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  overflow: hidden;
  transition: box-shadow var(--transition-base), border-color var(--transition-base);
}

#faq details:last-child {
  margin-bottom: 0;
}

#faq details[open] {
  box-shadow: 0 10px 30px -14px var(--color-shadow-strong);
  border-color: rgba(74, 159, 212, 0.4);
}

#faq summary {
  padding: var(--space-4) var(--space-5);
  font-weight: 600;
  font-size: 0.98rem;
  cursor: pointer;
  list-style: none;
  position: relative;
  padding-right: var(--space-8);
  color: var(--color-text);
  transition: background-color var(--transition-fast), color var(--transition-fast);
  user-select: none;
}

#faq summary::-webkit-details-marker {
  display: none;
}

#faq summary::after {
  content: "+";
  position: absolute;
  right: var(--space-5);
  top: 50%;
  transform: translateY(-50%);
  font-size: 1.3rem;
  font-weight: 400;
  line-height: 1;
  color: var(--color-accent);
  transition: transform var(--transition-base);
}

#faq details[open] summary::after {
  content: "−";
  transform: translateY(-50%) rotate(180deg);
}

#faq summary:hover {
  background: rgba(74, 159, 212, 0.08);
  color: var(--color-primary-light);
}

[data-theme="dark"] #faq summary:hover,
html.dark #faq summary:hover,
body.dark #faq summary:hover {
  color: var(--color-accent);
}

#faq details p {
  padding: 0 var(--space-5) var(--space-4);
  margin: 0;
  font-size: 0.94rem;
  animation: fadeSlideIn var(--transition-slow) both;
}

#contact address {
  padding: var(--space-5);
  border-radius: var(--radius-lg);
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  margin-bottom: var(--space-5);
}

#contact address p {
  margin-bottom: var(--space-2);
  font-size: 0.95rem;
}

#contact address p:last-child {
  margin-bottom: 0;
}

#sitemap ul,
#links ul {
  list-style: none;
  padding: 0;
  margin: 0;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
  gap: var(--space-2);
}

#sitemap li,
#links li {
  margin: 0;
}

#sitemap a,
#links a {
  display: block;
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-md);
  font-size: 0.92rem;
  background: var(--color-bg-alt);
  border: 1px solid transparent;
  transition: background-color var(--transition-fast), border-color var(--transition-fast), transform var(--transition-fast), color var(--transition-fast);
}

#sitemap a:hover,
#links a:hover {
  background: var(--color-surface);
  border-color: var(--color-accent);
  transform: translateY(-2px);
  text-decoration: none;
  color: var(--color-primary-light);
}

[data-theme="dark"] #sitemap a:hover,
[data-theme="dark"] #links a:hover {
  color: var(--color-accent);
}

footer {
  margin-top: var(--space-8);
  padding: var(--space-7) var(--space-5) var(--space-6);
  background: linear-gradient(180deg, var(--color-bg-alt), var(--color-bg));
  border-top: 1px solid var(--color-border);
}

footer > section,
footer > p {
  max-width: var(--max-width);
  margin-left: auto;
  margin-right: auto;
}

footer > section {
  padding: var(--space-6);
  border-radius: var(--radius-xl);
  background: var(--color-surface-glass);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border: 1px solid var(--color-border);
  box-shadow: 0 12px 36px -18px var(--color-shadow-strong);
  margin-bottom: var(--space-5);
}

footer h2 {
  font-size: 1.15rem;
  padding-bottom: var(--space-2);
}

footer h2::after {
  width: 40px;
  height: 3px;
}

footer p {
  font-size: 0.86rem;
  color: var(--color-text-muted);
  margin-bottom: var(--space-2);
}

footer > section p {
  color: var(--color-text-soft);
}

footer > p:last-of-type {
  margin-bottom: 0;
  padding-top: var(--space-3);
  border-top: 1px solid var(--color-border);
}

#back-to-top {
  position: fixed;
  right: var(--space-5);
  bottom: var(--space-5);
  z-index: 90;
  width: 48px;
  height: 48px;
  padding: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.72rem;
  font-weight: 700;
  line-height: 1.1;
  text-align: center;
  color: #fff;
  background: linear-gradient(135deg, var(--color-primary-light), var(--color-accent));
  border: none;
  border-radius: 50%;
  cursor: pointer;
  box-shadow: 0 10px 28px -8px rgba(46, 111, 158, 0.6);
  transition: transform var(--transition-base), box-shadow var(--transition-base), filter var(--transition-base);
  opacity: 0.92;
}

#back-to-top:hover {
  transform: translateY(-4px) scale(1.05);
  box-shadow: 0 16px 36px -10px rgba(46, 111, 158, 0.7);
  filter: brightness(1.1);
  opacity: 1;
}

#back-to-top:active {
  transform: translateY(-1px) scale(1);
}

@keyframes fadeSlideIn {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fadeUp {
  from {
    opacity: 0;
    transform: translateY(24px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes floatSoft {
  0%, 100% {
    transform: translateY(0);
  }
  50% {
    transform: translateY(-8px);
  }
}

@keyframes gradientShift {
  0% {
    background-position: 0% 50%;
  }
  50% {
    background-position: 100% 50%;
  }
  100% {
    background-position: 0% 50%;
  }
}

@supports (animation-timeline: view()) {
  main > section {
    animation: fadeUp linear both;
    animation-timeline: view();
    animation-range: entry 0% cover 22%;
  }

  #hero {
    animation: none;
  }
}

@supports not (animation-timeline: view()) {
  main > section {
    animation: fadeUp 0.7s cubic-bezier(0.22, 0.61, 0.36, 1) both;
  }

  main > section:nth-of-type(1) { animation-delay: 0.02s; }
  main > section:nth-of-type(2) { animation-delay: 0.06s; }
  main > section:nth-of-type(3) { animation-delay: 0.10s; }
  main > section:nth-of-type(4) { animation-delay: 0.14s; }
  main > section:nth-of-type(5) { animation-delay: 0.18s; }
  main > section:nth-of-type(6) { animation-delay: 0.22s; }
  main > section:nth-of-type(7) { animation-delay: 0.26s; }
  main > section:nth-of-type(8) { animation-delay: 0.30s; }
  main > section:nth-of-type(9) { animation-delay: 0.34s; }
  main > section:nth-of-type(10) { animation-delay: 0.38s; }
}

@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;
  }
}

@media (max-width: 1024px) {
  #hero {
    grid-template-columns: 1fr;
    padding: var(--space-7) var(--space-5);
    gap: var(--space-6);
  }

  #hero figure {
    max-width: 640px;
    margin: 0 auto;
  }

  header form[role="search"] {
    flex: 1 1 220px;
  }
}

@media (max-width: 860px) {
  :root {
    --header-height: 64px;
  }

  header > div {
    padding: var(--space-2) var(--space-4);
    gap: var(--space-2);
  }

  header nav {
    order: 4;
    flex-basis: 100%;
    max-height: 0;
    overflow: hidden;
    transition: max-height var(--transition-slow);
  }

  header nav[aria-hidden="false"],
  header nav.is-open {
    max-height: 480px;
  }

  header nav ul {
    flex-direction: column;
    align-items: stretch;
    padding: var(--space-2) 0;
    gap: var(--space-1);
  }

  header nav a {
    display: block;
    padding: var(--space-3) var(--space-4);
    border-radius: var(--radius-md);
  }

  header form[role="search"] {
    order: 5;
    flex-basis: 100%;
    max-width: none;
  }

  #menu-toggle {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    margin-left: auto;
  }

  main {
    padding: var(--space-5) var(--space-4) var(--space-7);
    gap: var(--space-6);
  }

  #about,
  #products,
  #solutions,
  #cases,
  #news,
  #articles,
  #howto,
  #faq,
  #contact,
  #sitemap,
  #links {
    padding: var(--space-6) var(--space-4);
    border-radius: var(--radius-lg);
  }

  #hero {
    border-radius: var(--radius-lg);
    padding: var(--space-6) var(--space-4);
  }

  #hero p:last-child a {
    flex: 1 1 auto;
  }

  blockquote {
    padding: var(--space-4);
  }

  #back-to-top {
    width: 44px;
    height: 44px;
    right: var(--space-4);
    bottom: var(--space-4);
  }
}

@media (max-width: 520px) {
  body {
    font-size: 15px;
    line-height: 1.7;
  }

  h2::after {
    width: 44px;
    height: 3px;
  }

  header > div > a[aria-label="中国X站首页"] {
    font-size: 1.05rem;
    padding: var(--space-1) var(--space-2);
  }

  header form[role="search"] button {
    padding: var(--space-2) var(--space-3);
  }

  #theme-toggle,
  #menu-toggle {
    padding: var(--space-2) var(--space-3);
    font-size: 0.8rem;
  }

  #hero p:last-child {
    flex-direction: column;
  }

  #hero p:last-child a {
    width: 100%;
  }

  #news article,
  #articles article {
    padding: var(--space-4);
  }

  #howto ol li {
    padding-left: var(--space-7);
  }

  #sitemap ul,
  #links ul {
    grid-template-columns: 1fr 1fr;
  }

  footer {
    padding: var(--space-6) var(--space-4) var(--space-5);
  }

  footer > section {
    padding: var(--space-4);
    border-radius: var(--radius-lg);
  }
}

@media (hover: none) {
  #hero figure:hover,
  #news article:hover,
  #articles article:hover,
  #sitemap a:hover,
  #links a:hover,
  #back-to-top:hover {
    transform: none;
  }
}

@media print {
  header,
  #back-to-top,
  #theme-toggle,
  #menu-toggle,
  header form[role="search"] {
    display: none !important;
  }

  body {
    background: #fff;
    color: #000;
  }

  main {
    max-width: none;
    padding: 0;
  }

  main > section {
    box-shadow: none;
    border: 1px solid #ccc;
    break-inside: avoid;
    page-break-inside: avoid;
  }

  a {
    color: #000;
    text-decoration: underline;
  }

  a[href^="http"]::after {
    content: " (" attr(href) ")";
    font-size: 0.8em;
    word-break: break-all;
  }
}