:root {
  --bg: #f3f8fd;
  --bg-strong: #ffffff;
  --text: #163247;
  --muted: #5f7a93;
  --line: rgba(94, 142, 183, 0.18);
  --accent: #2d84d8;
  --accent-soft: #d9ebfb;
  --shadow: 0 20px 45px rgba(48, 88, 126, 0.12);
  --radius: 24px;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Segoe UI", "Noto Sans TC", sans-serif;
  color: var(--text);
  background:
    radial-gradient(circle at top left, rgba(133, 193, 255, 0.3), transparent 24%),
    linear-gradient(180deg, #fbfdff 0%, var(--bg) 100%);
}

a {
  color: inherit;
  text-decoration: none;
}

.hero,
.section,
.reader-header,
.reader-layout {
  max-width: 1120px;
  margin: 0 auto;
  padding-left: 24px;
  padding-right: 24px;
}

.top-nav,
.reader-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
  padding-top: 24px;
}

.brand {
  font-weight: 700;
}

.top-nav a:not(.brand) {
  color: var(--muted);
}

.hero {
  padding-top: 12px;
  padding-bottom: 56px;
}

.hero-panel,
.card,
.sidebar {
  background: rgba(255, 255, 255, 0.84);
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
  backdrop-filter: blur(10px);
}

.hero-panel {
  margin-top: 44px;
  padding: 48px;
  border-radius: 36px;
}

.eyebrow,
.chapter-number {
  color: var(--accent);
  font-size: 0.85rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

h1,
h2,
h3 {
  line-height: 1.2;
  margin: 0;
}

h1 {
  margin-top: 12px;
  max-width: 780px;
  font-size: clamp(2.4rem, 6vw, 4.6rem);
}

.lead,
.card p,
.sidebar-link,
.chapter-card p {
  color: var(--muted);
  line-height: 1.8;
}

.hero-actions {
  display: flex;
  gap: 12px;
  margin-top: 24px;
  flex-wrap: wrap;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 12px 18px;
  border-radius: 999px;
  border: 1px solid var(--line);
}

.button.primary {
  color: white;
  background: var(--text);
}

.button.secondary {
  background: var(--bg-strong);
}

.button.small {
  padding: 9px 14px;
}

.section {
  padding-top: 20px;
  padding-bottom: 20px;
}

.section-heading {
  margin-bottom: 20px;
}

.feature-grid,
.chapter-list {
  display: grid;
  gap: 18px;
}

.feature-grid {
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
}

.chapter-list {
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
}

.card {
  border-radius: var(--radius);
  padding: 24px;
}

.reader-layout {
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
  gap: 24px;
  padding-top: 20px;
  padding-bottom: 48px;
}

.sidebar {
  border-radius: var(--radius);
  padding: 20px;
  position: sticky;
  top: 24px;
  align-self: start;
}

.sidebar-link {
  display: block;
  padding: 12px;
  border-radius: 14px;
}

.sidebar-link.active {
  background: var(--accent-soft);
  color: var(--text);
}

.reader-content {
  display: grid;
  gap: 18px;
}

.reader-block h2,
.cta-card h2 {
  margin-bottom: 10px;
}

.reader-block h3 {
  margin-top: 18px;
  margin-bottom: 8px;
}

.reader-block p + p {
  margin-top: 12px;
}

.reader-code {
  margin: 16px 0 0;
  padding: 18px;
  border-radius: 18px;
  overflow-x: auto;
  background: #eff6fd;
  color: #234969;
}

.reader-code code {
  font-family: Consolas, "Courier New", monospace;
  font-size: 0.95rem;
  line-height: 1.7;
  white-space: pre;
}

.reader-content code:not(.reader-code code) {
  font-family: Consolas, "Courier New", monospace;
  background: #eff6fd;
  color: #234969;
  padding: 0.12rem 0.35rem;
  border-radius: 8px;
}

.reader-list {
  margin: 16px 0 0;
  padding-left: 20px;
  color: var(--muted);
  line-height: 1.9;
}

.cta-card {
  background: linear-gradient(135deg, #eef7ff 0%, #ffffff 100%);
}

@media (max-width: 920px) {
  .reader-layout {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
  }

  .hero-panel {
    padding: 32px 24px;
  }
}

@media (max-width: 640px) {
  .hero,
  .section,
  .reader-header,
  .reader-layout {
    padding-left: 16px;
    padding-right: 16px;
  }

  .top-nav,
  .reader-header {
    flex-wrap: wrap;
  }
}