:root {
  --bg: #eef6ff;
  --text: #1f2937;
  --muted: #64748b;
  --line: #dbeafe;
  --card: #ffffff;
  --primary: #1e3a8a;
  --primary-2: #0f766e;
  --soft: #f0f9ff;
  --code: #0f172a;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial, "Microsoft YaHei", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.75;
}

a {
  color: inherit;
}

.page {
  max-width: 1220px;
  margin: 0 auto;
  padding: 40px 20px 90px;
}

.hero {
  display: grid;
  grid-template-columns: 1.05fr 0.95fr;
  gap: 28px;
  align-items: center;
  margin-bottom: 26px;
}

.hero-card,
.card,
.lesson-card,
.code-card {
  background: var(--card);
  border: 1px solid var(--line);
  box-shadow: 0 12px 34px rgba(30, 58, 138, 0.08);
}

.hero-card {
  border-radius: 28px;
  padding: 34px;
}

.hero h1 {
  margin: 0 0 12px;
  font-size: 38px;
  line-height: 1.22;
}

.hero p {
  margin: 0;
  color: var(--muted);
}

.hero img {
  width: 100%;
  display: block;
  border-radius: 28px;
  border: 1px solid var(--line);
}

.nav {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin: 22px 0 32px;
}

.nav a {
  text-decoration: none;
  background: #fff;
  border: 1px solid #bfdbfe;
  padding: 10px 14px;
  border-radius: 999px;
  color: var(--primary);
  font-size: 14px;
}

.nav a:hover {
  background: var(--primary);
  color: #fff;
}

.card,
.code-card {
  border-radius: 22px;
  padding: 24px;
  margin-bottom: 22px;
}

.card h2,
.code-card h2 {
  margin: 0 0 14px;
  font-size: 24px;
}

.card h3,
.code-card h3 {
  margin: 22px 0 10px;
  font-size: 18px;
}

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

.path,
.tag-list {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.path span,
.tag-list span {
  background: var(--soft);
  border: 1px solid #bfdbfe;
  color: var(--primary);
  border-radius: 999px;
  padding: 8px 12px;
  font-size: 14px;
}

.lesson-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 18px;
}

.lesson-card {
  border-radius: 22px;
  padding: 20px;
  text-decoration: none;
}

.lesson-card:hover {
  transform: translateY(-3px);
}

.lesson-card strong {
  display: block;
  margin-bottom: 8px;
  font-size: 18px;
}

.lesson-card span {
  color: var(--muted);
  font-size: 14px;
}

.code-grid {
  display: grid;
  gap: 18px;
}

.code-title {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 10px;
  margin-bottom: 10px;
}

.code-title h3 {
  margin: 0;
  font-size: 18px;
}

.badge {
  display: inline-flex;
  align-items: center;
  min-height: 26px;
  padding: 0 10px;
  border-radius: 999px;
  background: #ecfeff;
  border: 1px solid #99f6e4;
  color: #0f766e;
  font-size: 12px;
}

.code {
  background: var(--code);
  color: #e5e7eb;
  padding: 18px;
  border-radius: 14px;
  overflow-x: auto;
  font-family: Consolas, Monaco, "Courier New", monospace;
  font-size: 14px;
  white-space: pre;
  line-height: 1.65;
}

.code-note {
  background: #f8fafc;
  border: 1px solid #e2e8f0;
  border-radius: 14px;
  padding: 14px;
  color: #475569;
  margin-top: 12px;
}

.checklist {
  display: grid;
  gap: 10px;
  padding: 0;
  margin: 0;
  list-style: none;
}

.checklist li {
  padding: 12px 14px;
  background: var(--soft);
  border: 1px solid #bfdbfe;
  border-radius: 14px;
}

.checklist li::before {
  content: "✓ ";
  color: #16a34a;
  font-weight: 700;
}

.summary-box {
  background: linear-gradient(135deg, var(--primary), var(--primary-2));
  color: #ffffff;
  border-radius: 22px;
  padding: 24px;
  margin-top: 22px;
}

.summary-box h2 {
  margin-top: 0;
}

.summary-box p {
  color: #e0f2fe;
}

.warning {
  background: #fff7ed;
  border: 1px solid #fed7aa;
  color: #9a3412;
  border-radius: 18px;
  padding: 16px;
  margin-bottom: 22px;
}

.note {
  color: var(--muted);
}

.two-col {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 18px;
}

@media (max-width: 920px) {
  .hero,
  .two-col {
    grid-template-columns: 1fr;
  }

  .lesson-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 560px) {
  .page {
    padding: 28px 16px 70px;
  }

  .hero h1 {
    font-size: 28px;
  }

  .hero-card,
  .card,
  .code-card {
    padding: 20px;
  }

  .lesson-grid {
    grid-template-columns: 1fr;
  }
}