:root {
  --bg: #ffffff;
  --bg-soft: #f5f5f7;
  --text: #1d1d1f;
  --text-soft: #6e6e73;
  --border: #e3e3e6;
  --accent: #8b5cf6;
  --accent-soft: #ede9fe;
  --shadow: 0 4px 24px rgba(0, 0, 0, 0.06);
  --radius: 16px;
  --max-width: 920px;
}

[data-theme="dark"] {
  --bg: #161618;
  --bg-soft: #1f1f23;
  --text: #f5f5f7;
  --text-soft: #9a9aa0;
  --border: #2c2c31;
  --accent: #a78bfa;
  --accent-soft: #2c2740;
  --shadow: 0 4px 24px rgba(0, 0, 0, 0.4);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family:
    "Geist", "PingFang SC", "Microsoft YaHei", system-ui, -apple-system,
    sans-serif;
  line-height: 1.7;
  transition: background 0.2s ease, color 0.2s ease;
}

.float-controls {
  position: fixed;
  top: 16px;
  right: 16px;
  z-index: 20;
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 6px;
  background: color-mix(in srgb, var(--bg) 80%, transparent);
  backdrop-filter: blur(12px);
  border: 1px solid var(--border);
  border-radius: 999px;
  box-shadow: var(--shadow);
}

#theme-toggle {
  display: grid;
  place-items: center;
  width: 34px;
  height: 34px;
  border: none;
  background: transparent;
  border-radius: 50%;
  cursor: pointer;
  color: var(--text);
  line-height: 0;
  transition: background 0.2s ease;
}

#theme-toggle:hover {
  background: var(--accent-soft);
}

#theme-toggle img {
  display: block;
}

[data-theme="dark"] #theme-toggle img {
  filter: invert(1);
}

.lang-switch {
  display: flex;
  align-items: center;
  gap: 2px;
}

.lang-switch a {
  display: grid;
  place-items: center;
  width: 34px;
  height: 34px;
  border-radius: 50%;
  color: var(--text-soft);
  text-decoration: none;
  font-size: 13px;
  font-weight: 600;
  transition: background 0.2s ease, color 0.2s ease;
}

.lang-switch a:hover {
  background: var(--bg-soft);
}

.lang-switch a.active {
  background: var(--accent);
  color: #fff;
}

main {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 24px 20px 72px;
}

.hero {
  position: relative;
  text-align: center;
  padding: 24px 0 48px;
  overflow: hidden;
  background: linear-gradient(to bottom, var(--accent-soft), transparent 85%);
}

.hero h1 {
  font-size: 64px;
  letter-spacing: 0.08em;
  margin: 0 0 8px;
  font-weight: 700;
}

.hero .roman {
  color: var(--text-soft);
  font-size: 18px;
  margin: 0 0 20px;
  letter-spacing: 0.05em;
}

.hero-chars {
  display: flex;
  justify-content: center;
  align-items: flex-end;
  gap: 20px;
  margin: 12px 0 24px;
}

.hero-char {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 6px;
}

.hero-pinyin {
  color: var(--text-soft);
  font-size: 20px;
  letter-spacing: 0.03em;
}

.hero-hanzi {
  font-size: 64px;
  font-weight: 700;
  line-height: 1.1;
}

.float-toc {
  position: fixed;
  right: 20px;
  top: 50%;
  transform: translateY(-50%);
  z-index: 20;
  width: 46px;
  height: 46px;
  padding: 6px;
  background: color-mix(in srgb, var(--bg) 80%, transparent);
  backdrop-filter: blur(12px);
  border: 1px solid var(--border);
  border-radius: 14px;
  box-shadow: var(--shadow);
}

#toc-toggle {
  display: grid;
  place-items: center;
  width: 100%;
  height: 100%;
  border: none;
  background: transparent;
  border-radius: 10px;
  cursor: pointer;
  color: var(--text);
  line-height: 0;
  transition: background 0.2s ease;
}

#toc-toggle:hover {
  background: var(--accent-soft);
}

#toc-toggle img {
  filter: brightness(0) saturate(100%) invert(38%) sepia(50%) saturate(4500%)
    hue-rotate(245deg) brightness(95%);
}

.toc-links {
  position: absolute;
  top: 50%;
  right: calc(100% + 8px);
  display: flex;
  flex-direction: column;
  gap: 2px;
  padding: 8px;
  min-width: 120px;
  background: color-mix(in srgb, var(--bg) 92%, transparent);
  backdrop-filter: blur(12px);
  border: 1px solid var(--border);
  border-radius: 14px;
  box-shadow: var(--shadow);
  opacity: 0;
  transform: translateY(-50%) scale(0.85);
  transform-origin: top right;
  pointer-events: none;
  transition: opacity 0.2s ease, transform 0.2s ease;
}

.float-toc.open .toc-links {
  opacity: 1;
  transform: translateY(-50%) scale(1);
  pointer-events: auto;
}

.toc-links a {
  display: flex;
  align-items: center;
  gap: 6px;
  color: var(--text-soft);
  text-decoration: none;
  font-size: 13px;
  padding: 5px 10px;
  border-radius: 8px;
  transition: color 0.2s ease, background 0.2s ease;
  white-space: nowrap;
}

.toc-links a img {
  flex-shrink: 0;
}

[data-theme="dark"] .toc-links a img {
  filter: invert(1);
}

[data-theme="dark"] .origin-line img,
[data-theme="dark"] .back-top img {
  filter: invert(1);
}

.toc-links a:hover {
  color: var(--accent);
  background: var(--accent-soft);
}

.toc-links a.active {
  color: #fff;
  background: var(--accent);
  font-weight: 600;
}

.toc-links a.active img {
  filter: invert(1);
}

.section {
  margin-bottom: 56px;
  scroll-margin-top: 24px;
}

.section-head {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 20px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--border);
}

.section-head h2 {
  font-size: 22px;
  margin: 0;
}

.section-head h2 a {
  color: inherit;
  text-decoration: none;
}

.section-head h2 a::after {
  content: "";
  display: inline-block;
  width: 15px;
  height: 15px;
  margin-left: 8px;
  vertical-align: middle;
  position: relative;
  top: -4px;
  background-color: var(--text-soft);
  -webkit-mask: url("/assets/icons/hash.svg") center / contain no-repeat;
  mask: url("/assets/icons/hash.svg") center / contain no-repeat;
  opacity: 0;
  transition: opacity 0.15s ease;
}

.section-head:hover h2 a::after,
.section-head h2 a:focus-visible::after {
  opacity: 0.6;
}

.section-index {
  margin-left: auto;
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.1em;
  color: var(--text-soft);
  opacity: 0.6;
}

.section-icon {
  display: grid;
  place-items: center;
  width: 38px;
  height: 38px;
  border-radius: 11px;
  background: var(--accent-soft);
  color: var(--accent);
  flex-shrink: 0;
}

.section-icon img {
  filter: brightness(0) saturate(100%) invert(38%) sepia(50%) saturate(4500%)
    hue-rotate(245deg) brightness(95%);
}

.card {
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
  margin-bottom: 28px;
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}

.card:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
  border-color: var(--accent);
}

.origin-line {
  display: flex;
  align-items: center;
  gap: 10px;
  margin: 0 0 16px;
  padding: 10px 16px;
  border-left: 3px solid var(--accent);
  background: var(--bg);
  border-radius: 0 10px 10px 0;
  color: var(--accent);
  font-size: 15px;
  font-weight: 600;
}

.origin-text {
  line-height: 1.4;
}

.card p {
  margin: 0 0 12px;
}

.card p:last-child {
  margin-bottom: 0;
}

.lead {
  font-size: 17px;
}

.example {
  position: relative;
  padding: 14px 18px;
  margin-top: 12px;
  border-left: 3px solid var(--accent);
  background: var(--accent-soft);
  border-radius: 8px;
  font-size: 15px;
}

.tip {
  background: linear-gradient(135deg, var(--accent-soft), var(--bg-soft));
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px 24px;
  box-shadow: var(--shadow);
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}

.tip:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
  border-color: var(--accent);
}

.tip p {
  margin: 0;
}

.site-footer {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 20px;
  border-top: 1px solid var(--border);
  color: var(--text-soft);
  font-size: 13px;
  text-align: center;
}

.back-top {
  position: fixed;
  right: 24px;
  bottom: 24px;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  cursor: pointer;
  display: grid;
  place-items: center;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.2s ease, transform 0.2s ease, background 0.2s ease;
}

.back-top.visible {
  opacity: 1;
  pointer-events: auto;
}

.back-top:hover {
  transform: translateY(-2px);
  background: var(--bg-soft);
}

@media (max-width: 640px) {
  .hero h1 {
    font-size: 40px;
  }
  .hero-chars {
    gap: 12px;
  }
  .hero-hanzi {
    font-size: 44px;
  }
  .hero-pinyin {
    font-size: 17px;
  }
  .float-toc {
    right: 10px;
    padding: 6px;
  }
  .toc-links a {
    padding: 4px 8px;
    font-size: 12px;
  }
}