:root {
  --bg: #f3f7f9;
  --ink: #112129;
  --primary: #0c6c84;
  --accent: #f0a500;
  --card: #ffffff;
  --muted: #5a6a72;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Noto Sans SC", "Microsoft YaHei", sans-serif;
  color: var(--ink);
  background: radial-gradient(circle at top right, #d9f3f7 0%, var(--bg) 42%, #eef5f6 100%);
}

.hero {
  padding: 1.2rem 8vw 4rem;
  background: linear-gradient(130deg, #073341, #0c6c84 58%, #31a8bb);
  color: #fff;
}

.nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 3rem;
}

.nav .logo {
  font-weight: 800;
  letter-spacing: 0.06em;
}

.nav ul {
  list-style: none;
  display: flex;
  gap: 1.1rem;
  padding: 0;
  margin: 0;
}

.nav a {
  color: #fff;
  text-decoration: none;
}

.hero-content h1 {
  margin: 0.5rem 0;
  font-size: clamp(1.8rem, 3vw, 2.9rem);
}

.tag {
  display: inline-block;
  padding: 0.3rem 0.7rem;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.2);
  font-size: 0.9rem;
}

.cta {
  display: inline-block;
  margin-top: 1rem;
  padding: 0.65rem 1rem;
  background: var(--accent);
  color: #1f252b;
  border-radius: 10px;
  text-decoration: none;
  font-weight: 700;
}

.section {
  width: min(1100px, 90vw);
  margin: 2.8rem auto;
}

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

.timeline article,
.quiz-box,
.card {
  background: var(--card);
  border-radius: 14px;
  padding: 1rem;
  box-shadow: 0 8px 20px rgba(13, 42, 54, 0.08);
}

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

.card h3 {
  margin-top: 0;
}

.card p {
  color: var(--muted);
  line-height: 1.5;
}

.choices {
  display: grid;
  gap: 0.7rem;
  margin: 0.7rem 0 1rem;
}

.choice {
  border: 1px solid #c3d5db;
  background: #f8fcfd;
  padding: 0.7rem;
  border-radius: 10px;
  cursor: pointer;
}

.choice.correct {
  border-color: #0e8a51;
  background: #e9fff4;
}

.choice.wrong {
  border-color: #c13838;
  background: #fff0f0;
}

.btn {
  border: none;
  border-radius: 10px;
  background: var(--primary);
  color: #fff;
  padding: 0.65rem 1rem;
  cursor: pointer;
}

.score {
  font-weight: 700;
}

footer {
  text-align: center;
  color: #48606a;
  padding: 1.5rem;
}

@media (max-width: 640px) {
  .nav {
    flex-direction: column;
    gap: 1rem;
  }

  .nav ul {
    flex-wrap: wrap;
    justify-content: center;
  }
}