:root {
  --bg-color: #0f172a;
  --card-bg: #1e293b;
  --text-main: #f8fafc;
  --text-muted: #94a3b8;
  --accent: #38bdf8;
  --accent-hover: #0284c7;
}

body {
  margin: 0;
  padding: 0;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  background-color: var(--bg-color);
  color: var(--text-main);
  min-height: 100vh;
}

header {
  background-color: rgba(30, 41, 59, 0.8);
  backdrop-filter: blur(8px);
  padding: 1.5rem 2rem;
  border-bottom: 1px solid #334155;
  position: sticky;
  top: 0;
  z-index: 10;
}

header h1 {
  margin: 0;
  font-size: 1.5rem;
  color: var(--accent);
}

main {
  max-width: 1200px;
  margin: 0 auto;
  padding: 2rem;
}

/* Category Filter Bar */
.filter-bar {
  display: flex;
  gap: 0.75rem;
  margin-bottom: 2rem;
  flex-wrap: wrap;
}

.filter-btn {
  background: #1e293b;
  color: var(--text-muted);
  border: 1px solid #334155;
  padding: 8px 16px;
  border-radius: 20px;
  cursor: pointer;
  font-size: 0.9rem;
  transition: all 0.2s ease;
}

.filter-btn:hover, 
.filter-btn.active {
  background: var(--accent);
  color: #0f172a;
  border-color: var(--accent);
  font-weight: bold;
}

/* Catalog Grid */
.catalog-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 2rem;
}

.book-card {
  background-color: var(--card-bg);
  border-radius: 12px;
  overflow: hidden;
  border: 1px solid #334155;
  cursor: pointer;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.book-card:hover {
  transform: translateY(-4px);
  border-color: var(--accent);
  box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.5);
}

.cover-container {
  width: 100%;
  height: 280px;
  background-color: #334155;
}

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

.book-info {
  padding: 1rem;
}

.book-info h3 {
  margin: 0 0 0.5rem 0;
  font-size: 1.1rem;
}

.book-info p {
  margin: 0 0 0.5rem 0;
  font-size: 0.9rem;
  color: var(--text-muted);
}

.category-badge {
  display: inline-block;
  background: #334155;
  color: var(--accent);
  font-size: 0.75rem;
  padding: 2px 8px;
  border-radius: 4px;
}

.status-msg {
  grid-column: 1 / -1;
  text-align: center;
  color: var(--text-muted);
  padding: 3rem 0;
}