:root {
  --primary-color: #0d6efd;
  --secondary-color: #6c757d;
  --success-color: #198754;
  --danger-color: #dc3545;
  --warning-color: #ffc107;
  --info-color: #0dcaf0;
  --light-color: #f8f9fa;
  --dark-color: #212529;
}

body {
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  line-height: 1.6;
}

.hero-section {
  background: linear-gradient(135deg, var(--primary-color), var(--info-color));
  color: white;
  padding: 100px 0;
}

.card {
  transition: transform 0.3s ease, box-shadow 0.3s ease;
  border: none;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
}

.card:hover {
  transform: translateY(-5px);
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.15);
}

.book-card {
  height: 100%;
}

.book-card .card-img-top {
  height: 250px;
  object-fit: cover;
}

.btn-primary {
  background-color: var(--primary-color);
  border-color: var(--primary-color);
}

.btn-primary:hover {
  background-color: #0b5ed7;
  border-color: #0a58ca;
}

.navbar-brand {
  font-size: 1.5rem;
}

.category-filter {
  background-color: var(--light-color);
  border-radius: 10px;
  padding: 20px;
  margin-bottom: 30px;
}

.book-detail-image {
  max-height: 400px;
  object-fit: cover;
}

.thumbnail-images img {
  width: 80px;
  height: 80px;
  object-fit: cover;
  cursor: pointer;
  border: 2px solid transparent;
  border-radius: 5px;
  transition: border-color 0.3s ease;
}

.thumbnail-images img:hover,
.thumbnail-images img.active {
  border-color: var(--primary-color);
}

.cart-item {
  border-bottom: 1px solid #eee;
  padding: 15px 0;
}

.cart-item:last-child {
  border-bottom: none;
}

.admin-sidebar {
  min-height: calc(100vh - 56px);
  background-color: var(--dark-color);
}

.admin-sidebar .nav-link {
  color: rgba(255, 255, 255, 0.8);
  border-radius: 5px;
  margin: 2px 0;
}

.admin-sidebar .nav-link:hover,
.admin-sidebar .nav-link.active {
  background-color: var(--primary-color);
  color: white;
}

.stats-card {
  background: linear-gradient(135deg, var(--primary-color), var(--info-color));
  color: white;
  border-radius: 15px;
}

.loading {
  display: none;
  text-align: center;
  padding: 20px;
}

.loading.show {
  display: block;
}

@media (max-width: 768px) {
  .hero-section {
    padding: 50px 0;
  }

  .hero-section h1 {
    font-size: 2rem;
  }

  .book-card .card-img-top {
    height: 200px;
  }
}