* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Noto Sans KR", sans-serif;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  min-height: 100vh;
  padding: 20px;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
}

.main-header {
  text-align: center;
  color: white;
  margin-bottom: 50px;
  padding: 40px 20px;
}

.main-header h1 {
  font-size: 3rem;
  font-weight: 700;
  margin-bottom: 10px;
  text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
}

.subtitle {
  font-size: 1.2rem;
  opacity: 0.9;
}

.textbook-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 30px;
  padding: 20px;
}

.textbook-card {
  background: white;
  border-radius: 16px;
  overflow: hidden;
  text-decoration: none;
  color: inherit;
  transition: transform 0.3s ease, box-shadow 0.3s ease;
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.textbook-card:hover {
  transform: translateY(-8px);
  box-shadow: 0 12px 24px rgba(0, 0, 0, 0.2);
}

.card-image {
  width: 100%;
  height: 280px;
  overflow: hidden;
  background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
  display: flex;
  align-items: center;
  justify-content: center;
}

.card-image img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.card-content {
  padding: 24px;
  text-align: center;
}

.card-content h2 {
  font-size: 1.8rem;
  font-weight: 700;
  color: #333;
  margin-bottom: 8px;
}

.card-content p {
  font-size: 1rem;
  color: #666;
  font-weight: 500;
}

@media (max-width: 768px) {
  .main-header h1 {
    font-size: 2rem;
  }

  .textbook-grid {
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 20px;
  }

  .card-image {
    height: 220px;
  }
}