:root {
  --primary: #1a73e8;
  --primary-dark: #1557b0;
  --primary-light: #4a90e8;
  --accent: #fbbc04;
  --accent-alt: #34a853;
  --danger: #ea4335;
  --bg: #f5f7fb;
  --bg-alt: #ffffff;
  --surface: rgba(255, 255, 255, 0.72);
  --surface-solid: #ffffff;
  --text: #1f2933;
  --text-secondary: #52606d;
  --text-muted: #7b8794;
  --border: rgba(26, 115, 232, 0.14);
  --border-solid: #e2e8f0;
  --shadow-sm: 0 2px 8px rgba(26, 115, 232, 0.08);
  --shadow-md: 0 8px 24px rgba(26, 115, 232, 0.12);
  --shadow-lg: 0 16px 48px rgba(26, 115, 232, 0.16);
  --radius-sm: 10px;
  --radius-md: 16px;
  --radius-lg: 24px;
  --radius-full: 999px;
  --transition: 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  --gradient-hero: linear-gradient(135deg, #1a73e8 0%, #4a90e8 40%, #6fb1fc 100%);
  --gradient-accent: linear-gradient(135deg, #fbbc04 0%, #ff9d2e 100%);
  --gradient-surface: linear-gradient(160deg, rgba(255,255,255,0.9), rgba(232,240,254,0.7));
  --font-sans: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans SC", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0d1117;
    --bg-alt: #161b22;
    --surface: rgba(22, 27, 34, 0.72);
    --surface-solid: #161b22;
    --text: #e6edf3;
    --text-secondary: #b0bec9;
    --text-muted: #8899a6;
    --border: rgba(74, 144, 232, 0.22);
    --border-solid: #2d3742;
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.4);
    --shadow-md: 0 8px 24px rgba(0, 0, 0, 0.5);
    --shadow-lg: 0 16px 48px rgba(0, 0, 0, 0.6);
    --gradient-hero: linear-gradient(135deg, #0b3d91 0%, #1557b0 45%, #1a73e8 100%);
    --gradient-surface: linear-gradient(160deg, rgba(22,27,34,0.9), rgba(13,17,23,0.75));
  }
}

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

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.75;
  color: var(--text);
  background-color: var(--bg);
  background-image:
    radial-gradient(circle at 12% 8%, rgba(26, 115, 232, 0.08), transparent 42%),
    radial-gradient(circle at 88% 4%, rgba(251, 188, 4, 0.08), transparent 38%);
  background-attachment: fixed;
  overflow-x: hidden;
  transition: background-color var(--transition), color var(--transition);
}

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

a {
  color: var(--primary);
  text-decoration: none;
  transition: color var(--transition);
}

a:hover,
a:focus-visible {
  color: var(--primary-dark);
}

h1, h2, h3, h4 {
  line-height: 1.35;
  color: var(--text);
  font-weight: 700;
  letter-spacing: -0.01em;
}

h1 { font-size: clamp(1.75rem, 4vw, 2.6rem); }
h2 { font-size: clamp(1.4rem, 3vw, 2rem); }
h3 { font-size: clamp(1.1rem, 2.2vw, 1.35rem); }

p { color: var(--text-secondary); }

ul, ol {
  padding-left: 1.4em;
}

li { margin-bottom: 0.35em; }

/* ============ Header ============ */
header {
  position: sticky;
  top: 0;
  z-index: 100;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 1rem 1.5rem;
  padding: 0.85rem clamp(1rem, 4vw, 2.5rem);
  background: var(--surface);
  backdrop-filter: blur(18px) saturate(160%);
  -webkit-backdrop-filter: blur(18px) saturate(160%);
  border-bottom: 1px solid var(--border);
  box-shadow: var(--shadow-sm);
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-size: 1.2rem;
  color: var(--text);
  flex-shrink: 0;
}

.brand svg {
  filter: drop-shadow(0 2px 6px rgba(26, 115, 232, 0.35));
  transition: transform var(--transition);
}

.brand:hover svg {
  transform: rotate(-8deg) scale(1.05);
}

.brand strong {
  font-size: 1.25rem;
  background: var(--gradient-hero);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  color: var(--primary);
}

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

header nav ul {
  display: flex;
  flex-wrap: wrap;
  gap: 0.25rem 0.35rem;
  list-style: none;
  margin: 0;
  padding: 0;
}

header nav a {
  display: inline-block;
  padding: 0.4rem 0.75rem;
  font-size: 0.9rem;
  color: var(--text-secondary);
  border-radius: var(--radius-full);
  transition: background-color var(--transition), color var(--transition), transform var(--transition);
}

header nav a:hover,
header nav a:focus-visible {
  color: var(--primary);
  background: rgba(26, 115, 232, 0.1);
  transform: translateY(-1px);
}

header form[role="search"] {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  flex-shrink: 0;
}

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

header form[role="search"] input {
  width: clamp(140px, 18vw, 220px);
  padding: 0.5rem 1rem;
  font-size: 0.9rem;
  color: var(--text);
  background: var(--bg-alt);
  border: 1px solid var(--border-solid);
  border-radius: var(--radius-full);
  outline: none;
  transition: border-color var(--transition), box-shadow var(--transition);
}

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

header form[role="search"] input:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(26, 115, 232, 0.18);
}

header form[role="search"] button {
  padding: 0.5rem 1.1rem;
  font-size: 0.9rem;
  font-weight: 600;
  color: #fff;
  background: var(--gradient-hero);
  border: none;
  border-radius: var(--radius-full);
  cursor: pointer;
  transition: transform var(--transition), box-shadow var(--transition), filter var(--transition);
}

header form[role="search"] button:hover {
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
  filter: brightness(1.05);
}

/* ============ Main layout ============ */
main {
  display: block;
  max-width: 1200px;
  margin: 0 auto;
  padding: clamp(1rem, 3vw, 2rem) clamp(1rem, 4vw, 2.5rem) 3rem;
}

main > section {
  margin-bottom: clamp(1.5rem, 4vw, 2.75rem);
  padding: clamp(1.25rem, 3.5vw, 2.5rem);
  background: var(--surface);
  backdrop-filter: blur(14px) saturate(150%);
  -webkit-backdrop-filter: blur(14px) saturate(150%);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  transition: box-shadow var(--transition), transform var(--transition), border-color var(--transition);
  animation: fadeUp 0.7s cubic-bezier(0.22, 1, 0.36, 1) both;
}

main > section:hover {
  box-shadow: var(--shadow-md);
  border-color: rgba(26, 115, 232, 0.28);
}

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

/* Staggered entrance for consecutive sections */
main > section:nth-of-type(2) { animation-delay: 0.05s; }
main > section:nth-of-type(3) { animation-delay: 0.1s; }
main > section:nth-of-type(4) { animation-delay: 0.15s; }
main > section:nth-of-type(5) { animation-delay: 0.2s; }

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }
}

/* ============ Hero / Banner ============ */
#hero {
  position: relative;
  overflow: hidden;
  padding: clamp(2rem, 6vw, 4rem) clamp(1.25rem, 4vw, 3rem);
  background: var(--gradient-hero);
  border: none;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  color: #fff;
}

#hero::before {
  content: "";
  position: absolute;
  inset: 0;
  background:
    radial-gradient(circle at 82% 18%, rgba(251, 188, 4, 0.35), transparent 45%),
    radial-gradient(circle at 15% 90%, rgba(52, 168, 83, 0.3), transparent 40%);
  pointer-events: none;
}

#hero::after {
  content: "";
  position: absolute;
  top: -40%;
  right: -10%;
  width: 55%;
  height: 160%;
  background: rgba(255, 255, 255, 0.08);
  border-radius: 50%;
  transform: rotate(18deg);
  pointer-events: none;
}

#hero > * {
  position: relative;
  z-index: 1;
}

#hero h1 {
  margin-top: 0;
  color: #fff;
  text-shadow: 0 2px 16px rgba(0, 0, 0, 0.25);
}

#hero p {
  max-width: 62ch;
  color: rgba(255, 255, 255, 0.92);
  font-size: clamp(0.95rem, 1.6vw, 1.05rem);
}

#hero figure {
  margin: 1.75rem 0;
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: var(--shadow-lg);
  background: rgba(255, 255, 255, 0.9);
  transition: transform var(--transition);
}

#hero figure:hover {
  transform: scale(1.012);
}

#hero figcaption {
  padding: 0.7rem 1rem;
  font-size: 0.85rem;
  color: var(--text-secondary);
  background: var(--surface-solid);
}

/* ============ Anchor navigation ============ */
nav[aria-label="页面锚点导航"] {
  margin-bottom: clamp(1.5rem, 4vw, 2.75rem);
  padding: clamp(1rem, 2.5vw, 1.75rem);
  background: var(--gradient-surface);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
}

nav[aria-label="页面锚点导航"] h2 {
  margin-top: 0;
  font-size: 1.05rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

nav[aria-label="页面锚点导航"] ul {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  list-style: none;
  margin: 0;
  padding: 0;
}

nav[aria-label="页面锚点导航"] a {
  display: inline-block;
  padding: 0.35rem 0.9rem;
  font-size: 0.88rem;
  color: var(--text-secondary);
  background: var(--bg-alt);
  border: 1px solid var(--border-solid);
  border-radius: var(--radius-full);
  transition: all var(--transition);
}

nav[aria-label="页面锚点导航"] a:hover,
nav[aria-label="页面锚点导航"] a:focus-visible {
  color: #fff;
  background: var(--gradient-hero);
  border-color: transparent;
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

/* ============ Section headings ============ */
main > section > h2 {
  position: relative;
  margin-top: 0;
  padding-bottom: 0.6rem;
}

main > section > h2::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: 0;
  width: 56px;
  height: 4px;
  border-radius: var(--radius-full);
  background: var(--gradient-accent);
}

main > section h3 {
  margin-top: 1.6rem;
  color: var(--primary);
}

/* ============ Cards: articles, news, faq, details ============ */
article {
  margin: 1.25rem 0;
  padding: clamp(1rem, 2.5vw, 1.5rem);
  background: var(--bg-alt);
  border: 1px solid var(--border-solid);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition), box-shadow var(--transition), border-color var(--transition);
}

article:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
  border-color: rgba(26, 115, 232, 0.35);
}

article h3 {
  margin-top: 0;
  color: var(--text);
}

article p:first-of-type {
  font-size: 0.85rem;
  color: var(--text-muted);
}

article a {
  display: inline-block;
  margin-top: 0.4rem;
  padding: 0.4rem 1rem;
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--primary);
  background: rgba(26, 115, 232, 0.08);
  border-radius: var(--radius-full);
  transition: all var(--transition);
}

article a:hover {
  color: #fff;
  background: var(--gradient-hero);
  box-shadow: var(--shadow-sm);
}

/* ============ FAQ details ============ */
details {
  margin: 0.75rem 0;
  background: var(--bg-alt);
  border: 1px solid var(--border-solid);
  border-radius: var(--radius-md);
  overflow: hidden;
  transition: border-color var(--transition), box-shadow var(--transition);
}

details[open] {
  border-color: rgba(26, 115, 232, 0.4);
  box-shadow: var(--shadow-sm);
}

details summary {
  position: relative;
  padding: 0.9rem 2.75rem 0.9rem 1.1rem;
  font-weight: 600;
  color: var(--text);
  cursor: pointer;
  list-style: none;
  transition: background-color var(--transition), color var(--transition);
}

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

details summary::after {
  content: "+";
  position: absolute;
  right: 1.1rem;
  top: 50%;
  transform: translateY(-50%);
  font-size: 1.4rem;
  font-weight: 400;
  line-height: 1;
  color: var(--primary);
  transition: transform var(--transition);
}

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

details summary:hover {
  background: rgba(26, 115, 232, 0.06);
  color: var(--primary);
}

details p {
  margin: 0;
  padding: 0 1.1rem 1.1rem;
  font-size: 0.95rem;
  animation: fadeUp 0.35s ease both;
}

/* ============ Lists in contact / sitemap / friends ============ */
#contact ul,
#sitemap ul,
#friends ul {
  list-style: none;
  padding: 0;
  display: grid;
  gap: 0.5rem;
}

#contact ul li {
  padding: 0.55rem 0.9rem;
  background: var(--bg-alt);
  border-left: 3px solid var(--primary);
  border-radius: var(--radius-sm);
  font-size: 0.95rem;
  transition: transform var(--transition), box-shadow var(--transition);
}

#contact ul li:hover {
  transform: translateX(4px);
  box-shadow: var(--shadow-sm);
}

#sitemap ul,
#friends ul {
  grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
}

#sitemap a,
#friends a {
  display: block;
  padding: 0.5rem 0.9rem;
  font-size: 0.92rem;
  color: var(--text-secondary);
  background: var(--bg-alt);
  border: 1px solid var(--border-solid);
  border-radius: var(--radius-sm);
  transition: all var(--transition);
}

#sitemap a:hover,
#friends a:hover {
  color: var(--primary);
  border-color: var(--primary);
  transform: translateY(-2px);
  box-shadow: var(--shadow-sm);
}

/* ============ HowTo steps ============ */
#howto ol {
  counter-reset: step;
  list-style: none;
  padding: 0;
  display: grid;
  gap: 0.75rem;
}

#howto ol li {
  position: relative;
  padding: 0.9rem 1rem 0.9rem 3.2rem;
  background: var(--bg-alt);
  border: 1px solid var(--border-solid);
  border-radius: var(--radius-md);
  transition: transform var(--transition), box-shadow var(--transition);
}

#howto ol li::before {
  counter-increment: step;
  content: counter(step);
  position: absolute;
  left: 0.9rem;
  top: 50%;
  transform: translateY(-50%);
  width: 1.7rem;
  height: 1.7rem;
  display: grid;
  place-items: center;
  font-size: 0.85rem;
  font-weight: 700;
  color: #fff;
  background: var(--gradient-hero);
  border-radius: 50%;
  box-shadow: var(--shadow-sm);
}

#howto ol li:hover {
  transform: translateX(4px);
  box-shadow: var(--shadow-sm);
}

/* ============ Footer ============ */
footer {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1.5rem 2rem;
  padding: clamp(1.5rem, 4vw, 3rem) clamp(1rem, 4vw, 2.5rem);
  background: linear-gradient(180deg, var(--bg-alt), var(--bg));
  border-top: 1px solid var(--border);
}

footer section {
  min-width: 0;
}

footer h2 {
  margin: 0 0 0.6rem;
  font-size: 1rem;
  color: var(--text);
}

footer p {
  margin: 0.3rem 0;
  font-size: 0.88rem;
  color: var(--text-muted);
  line-height: 1.7;
}

footer a {
  color: var(--primary);
  font-weight: 500;
}

footer a:hover {
  text-decoration: underline;
}

/* ============ Responsive ============ */
@media (max-width: 900px) {
  header {
    gap: 0.75rem 1rem;
  }

  header nav {
    order: 3;
    flex-basis: 100%;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
    scrollbar-width: none;
  }

  header nav::-webkit-scrollbar {
    display: none;
  }

  header nav ul {
    flex-wrap: nowrap;
    width: max-content;
  }

  header nav a {
    white-space: nowrap;
  }

  header form[role="search"] {
    margin-left: auto;
  }
}

@media (max-width: 600px) {
  body {
    font-size: 15px;
  }

  header {
    padding: 0.7rem 1rem;
  }

  .brand strong {
    font-size: 1.1rem;
  }

  header form[role="search"] {
    flex-basis: 100%;
    order: 4;
  }

  header form[role="search"] input {
    flex: 1;
    width: auto;
  }

  main {
    padding: 1rem 0.9rem 2rem;
  }

  main > section {
    border-radius: var(--radius-md);
    padding: 1.1rem;
  }

  #hero {
    border-radius: var(--radius-md);
    padding: 1.75rem 1.1rem;
  }

  #hero figure {
    margin: 1.25rem 0;
  }

  nav[aria-label="页面锚点导航"] a {
    font-size: 0.82rem;
    padding: 0.3rem 0.7rem;
  }

  #sitemap ul,
  #friends ul {
    grid-template-columns: repeat(auto-fill, minmax(130px, 1fr));
  }

  footer {
    grid-template-columns: 1fr;
    gap: 1.25rem;
    padding: 1.5rem 1rem 2rem;
  }
}

/* ============ Focus visibility ============ */
a:focus-visible,
button:focus-visible,
summary:focus-visible,
input:focus-visible {
  outline: 3px solid rgba(26, 115, 232, 0.55);
  outline-offset: 2px;
  border-radius: var(--radius-sm);
}

/* ============ Selection ============ */
::selection {
  background: rgba(26, 115, 232, 0.25);
  color: var(--text);
}

/* ============ Scrollbar ============ */
::-webkit-scrollbar {
  width: 10px;
  height: 10px;
}

::-webkit-scrollbar-track {
  background: transparent;
}

::-webkit-scrollbar-thumb {
  background: rgba(26, 115, 232, 0.35);
  border-radius: var(--radius-full);
  border: 2px solid transparent;
  background-clip: padding-box;
}

::-webkit-scrollbar-thumb:hover {
  background: rgba(26, 115, 232, 0.6);
  background-clip: padding-box;
}

/* ============ Print ============ */
@media print {
  header,
  footer,
  nav[aria-label="页面锚点导航"],
  #hero figure {
    display: none;
  }

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

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