/* ===================================
   CSS Variables and Global Styles
   =================================== */

:root {
  /* Primary Colors */
  --color-primary: #2563eb;
  --color-primary-dark: #1e40af;
  --color-primary-light: #3b82f6;
  
  /* Secondary Colors */
  --color-secondary: #64748b;
  --color-secondary-dark: #475569;
  --color-secondary-light: #94a3b8;
  
  /* Status Colors */
  --color-success: #10b981;
  --color-error: #ef4444;
  --color-warning: #f59e0b;
  --color-info: #06b6d4;
  
  /* Background Colors */
  --color-bg-primary: #ffffff;
  --color-bg-secondary: #f8fafc;
  --color-bg-tertiary: #f1f5f9;
  --color-bg-overlay: rgba(0, 0, 0, 0.5);
  
  /* Text Colors */
  --color-text-primary: #0f172a;
  --color-text-secondary: #475569;
  --color-text-tertiary: #94a3b8;
  --color-text-inverse: #ffffff;
  
  /* Border Colors */
  --color-border: #e2e8f0;
  --color-border-dark: #cbd5e1;
  
  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
  
  /* Spacing */
  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;
  --spacing-2xl: 3rem;
  
  /* Border Radius */
  --radius-sm: 0.25rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --radius-xl: 1rem;
  --radius-full: 9999px;
  
  /* Typography */
  --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  --line-height-base: 1.6;
  --line-height-tight: 1.25;
  
  /* Transitions */
  --transition-fast: 150ms ease-in-out;
  --transition-base: 250ms ease-in-out;
  --transition-slow: 350ms ease-in-out;
}

/* Global Reset */
*, *::before, *::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

/* Base Styles */
html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-family);
  line-height: var(--line-height-base);
  color: var(--color-text-primary);
  background-color: var(--color-bg-secondary);
  min-height: 100vh;
}

/* Container */
.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--spacing-md);
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  line-height: var(--line-height-tight);
  font-weight: 600;
  margin-bottom: var(--spacing-md);
}

h1 { font-size: 2rem; }
h2 { font-size: 1.5rem; }
h3 { font-size: 1.25rem; }

p {
  margin-bottom: var(--spacing-md);
}

/* ===================================
   Header and Search Interface
   =================================== */

.header {
  background-color: var(--color-bg-primary);
  border-bottom: 1px solid var(--color-border);
  box-shadow: var(--shadow-sm);
  padding: var(--spacing-xl) 0;
  margin-bottom: var(--spacing-xl);
}

.app-title {
  color: var(--color-primary);
  margin-bottom: var(--spacing-sm);
}

.app-subtitle {
  color: var(--color-text-secondary);
  font-size: 1rem;
  margin-bottom: 0;
}

.main-content {
  padding-bottom: var(--spacing-2xl);
}

.section-title {
  color: var(--color-text-primary);
  margin-bottom: var(--spacing-lg);
  padding-bottom: var(--spacing-sm);
  border-bottom: 2px solid var(--color-primary);
}

/* Search Section */
.search-section {
  background-color: var(--color-bg-primary);
  padding: var(--spacing-xl);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  margin-bottom: var(--spacing-xl);
}

.search-bar {
  display: flex;
  gap: var(--spacing-md);
  margin-bottom: var(--spacing-lg);
}

.search-input {
  flex: 1;
  padding: var(--spacing-md);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: 1rem;
  font-family: var(--font-family);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.search-input:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

.search-input::placeholder {
  color: var(--color-text-tertiary);
}

.search-options {
  display: flex;
  gap: var(--spacing-lg);
  flex-wrap: wrap;
}

/* Form Elements */
.form-group {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
}

.form-group label {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-text-secondary);
}

.form-select,
.form-input {
  padding: var(--spacing-sm) var(--spacing-md);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: 0.875rem;
  font-family: var(--font-family);
  background-color: var(--color-bg-primary);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
  min-height: 44px;
}

.form-select:focus,
.form-input:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

/* Buttons */
.btn {
  padding: var(--spacing-md) var(--spacing-xl);
  border: none;
  border-radius: var(--radius-md);
  font-size: 1rem;
  font-weight: 500;
  font-family: var(--font-family);
  cursor: pointer;
  transition: all var(--transition-fast);
  min-height: 44px;
  min-width: 44px;
}

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

.btn-primary:hover {
  background-color: var(--color-primary-dark);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

.btn-primary:active {
  transform: translateY(0);
}

.btn-primary:disabled {
  background-color: var(--color-secondary-light);
  cursor: not-allowed;
  transform: none;
}

.btn-secondary {
  background-color: var(--color-secondary);
  color: var(--color-text-inverse);
}

.btn-secondary:hover {
  background-color: var(--color-secondary-dark);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

.btn-secondary:active {
  transform: translateY(0);
}

/* ===================================
   Genre Buttons and Filter Panel
   =================================== */

.genre-section {
  background-color: var(--color-bg-primary);
  padding: var(--spacing-xl);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  margin-bottom: var(--spacing-xl);
}

.genre-buttons {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-md);
}

.genre-btn {
  padding: var(--spacing-sm) var(--spacing-lg);
  background-color: var(--color-bg-tertiary);
  color: var(--color-text-primary);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-full);
  font-size: 0.875rem;
  font-weight: 500;
  font-family: var(--font-family);
  cursor: pointer;
  transition: all var(--transition-fast);
  min-height: 44px;
}

.genre-btn:hover {
  background-color: var(--color-primary);
  color: var(--color-text-inverse);
  border-color: var(--color-primary);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.genre-btn:active {
  transform: translateY(0);
}

/* Filter Section */
.filter-section {
  background-color: var(--color-bg-primary);
  padding: var(--spacing-xl);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  margin-bottom: var(--spacing-xl);
}

.filter-panel {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: var(--spacing-lg);
}

.filter-actions {
  grid-column: 1 / -1;
  display: flex;
  gap: var(--spacing-md);
  margin-top: var(--spacing-md);
}

/* ===================================
   Results Grid and Book Cards
   =================================== */

.results-section {
  margin-bottom: var(--spacing-xl);
}

.results-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: var(--spacing-lg);
  margin-bottom: var(--spacing-xl);
}

.book-card {
  background-color: var(--color-bg-primary);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  overflow: hidden;
  transition: all var(--transition-base);
  display: flex;
  flex-direction: column;
}

.book-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-xl);
}

.book-cover {
  width: 100%;
  height: 280px;
  object-fit: cover;
  background-color: var(--color-bg-tertiary);
}

.book-info {
  padding: var(--spacing-md);
  flex: 1;
  display: flex;
  flex-direction: column;
}

.book-title {
  font-size: 1rem;
  font-weight: 600;
  color: var(--color-text-primary);
  margin-bottom: var(--spacing-sm);
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
  line-height: 1.4;
}

.book-author {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  margin-bottom: var(--spacing-sm);
}

.book-meta {
  font-size: 0.75rem;
  color: var(--color-text-tertiary);
  margin-bottom: var(--spacing-md);
}

.book-actions {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
  padding: var(--spacing-md);
  padding-top: 0;
}

.btn-detail {
  padding: var(--spacing-sm) var(--spacing-md);
  background-color: var(--color-primary);
  color: var(--color-text-inverse);
  border: none;
  border-radius: var(--radius-md);
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-fast);
  min-height: 44px;
}

.btn-detail:hover {
  background-color: var(--color-primary-dark);
}

.select-list {
  padding: var(--spacing-sm) var(--spacing-md);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: 0.875rem;
  font-family: var(--font-family);
  background-color: var(--color-bg-primary);
  cursor: pointer;
  min-height: 44px;
}

.compare-checkbox {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  cursor: pointer;
  padding: var(--spacing-sm);
  min-height: 44px;
}

.compare-input {
  width: 20px;
  height: 20px;
  cursor: pointer;
}

/* ===================================
   Modals and Overlays
   =================================== */

.modal {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: center;
}

.modal-overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: var(--color-bg-overlay);
  z-index: 1001;
}

.modal-content {
  position: relative;
  background-color: var(--color-bg-primary);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-xl);
  max-width: 900px;
  width: 90%;
  max-height: 90vh;
  overflow-y: auto;
  padding: var(--spacing-xl);
  z-index: 1002;
}

.modal-wide {
  max-width: 1200px;
}

.modal-close {
  position: absolute;
  top: var(--spacing-md);
  right: var(--spacing-md);
  background: none;
  border: none;
  font-size: 2rem;
  color: var(--color-text-secondary);
  cursor: pointer;
  width: 44px;
  height: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-md);
  transition: all var(--transition-fast);
}

.modal-close:hover {
  background-color: var(--color-bg-tertiary);
  color: var(--color-text-primary);
}

/* Book Detail Modal */
.book-detail {
  display: grid;
  grid-template-columns: 250px 1fr;
  gap: var(--spacing-xl);
  margin-top: var(--spacing-xl);
}

.book-detail-sidebar {
  display: flex;
  flex-direction: column;
}

.detail-cover {
  width: 100%;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
}

.book-detail-main {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-lg);
}

.detail-title {
  font-size: 1.75rem;
  color: var(--color-text-primary);
  margin-bottom: var(--spacing-sm);
}

.detail-author {
  font-size: 1.125rem;
  color: var(--color-text-secondary);
  margin-bottom: 0;
}

.detail-meta {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
}

.detail-meta p {
  margin-bottom: 0;
  font-size: 0.875rem;
}

.detail-description h3,
.detail-subjects h3 {
  font-size: 1.125rem;
  margin-bottom: var(--spacing-md);
  color: var(--color-text-primary);
}

.detail-description p {
  color: var(--color-text-secondary);
  line-height: 1.7;
}

.subject-tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-sm);
}

.subject-tag {
  padding: var(--spacing-xs) var(--spacing-md);
  background-color: var(--color-bg-tertiary);
  color: var(--color-text-primary);
  border-radius: var(--radius-full);
  font-size: 0.75rem;
  font-weight: 500;
}

.detail-actions {
  margin-top: var(--spacing-md);
}

#detailAddToList {
  width: 100%;
  max-width: 300px;
}

/* Comparison Modal */
.comparison-table-wrapper {
  overflow-x: auto;
  margin-top: var(--spacing-lg);
}

.comparison-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.875rem;
}

.comparison-table thead {
  position: sticky;
  top: 0;
  background-color: var(--color-bg-primary);
  z-index: 10;
}

.comparison-table th,
.comparison-table td {
  padding: var(--spacing-md);
  text-align: left;
  border: 1px solid var(--color-border);
}

.comparison-table th {
  background-color: var(--color-primary);
  color: var(--color-text-inverse);
  font-weight: 600;
}

.comparison-table tbody tr:nth-child(even) {
  background-color: var(--color-bg-secondary);
}

.comparison-table tbody tr:hover {
  background-color: var(--color-bg-tertiary);
}

.comparison-table img {
  max-width: 100px;
  border-radius: var(--radius-md);
}

/* ===================================
   Statistics, Loading, and Error States
   =================================== */

.statistics-section {
  background-color: var(--color-bg-primary);
  padding: var(--spacing-xl);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  margin-bottom: var(--spacing-xl);
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: var(--spacing-lg);
  margin-bottom: var(--spacing-xl);
}

.stat-card {
  padding: var(--spacing-lg);
  background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-dark) 100%);
  color: var(--color-text-inverse);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  text-align: center;
  transition: transform var(--transition-fast);
}

.stat-card:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}

.stat-card h3 {
  font-size: 0.875rem;
  font-weight: 500;
  margin-bottom: var(--spacing-sm);
  opacity: 0.9;
}

.stat-value {
  font-size: 2rem;
  font-weight: 700;
  margin-bottom: 0;
}

.search-stats {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: var(--spacing-md);
  padding: var(--spacing-lg);
  background-color: var(--color-bg-tertiary);
  border-radius: var(--radius-md);
}

.search-stats p {
  margin-bottom: 0;
  font-size: 0.875rem;
}

/* Controls Section */
.controls-section {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: var(--spacing-lg);
  background-color: var(--color-bg-primary);
  padding: var(--spacing-xl);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-md);
  margin-bottom: var(--spacing-xl);
}

.export-controls,
.comparison-controls {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.export-controls h3 {
  font-size: 1rem;
  margin-bottom: var(--spacing-sm);
}

.export-controls {
  flex-direction: row;
  align-items: center;
}

/* Loading Spinner */
.loading-spinner {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: var(--color-bg-overlay);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  z-index: 2000;
}

.spinner {
  width: 60px;
  height: 60px;
  border: 4px solid var(--color-border);
  border-top-color: var(--color-primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

@keyframes spin {
  to {
    transform: rotate(360deg);
  }
}

.loading-spinner p {
  margin-top: var(--spacing-lg);
  color: var(--color-text-inverse);
  font-size: 1.125rem;
  font-weight: 500;
}

.results-grid.loading {
  opacity: 0.5;
  pointer-events: none;
}

/* Error Message */
.error-message {
  position: fixed;
  top: var(--spacing-xl);
  left: 50%;
  transform: translateX(-50%);
  max-width: 600px;
  width: 90%;
  padding: var(--spacing-lg);
  background-color: #fee;
  color: var(--color-error);
  border: 2px solid var(--color-error);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-xl);
  z-index: 3000;
  font-weight: 500;
  text-align: center;
}

.error-message.fade-in {
  animation: fadeIn 0.3s ease-in-out;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateX(-50%) translateY(-20px);
  }
  to {
    opacity: 1;
    transform: translateX(-50%) translateY(0);
  }
}

/* Pagination */
.pagination {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: var(--spacing-md);
  margin-top: var(--spacing-xl);
  padding: var(--spacing-lg);
}

.pagination button {
  padding: var(--spacing-sm) var(--spacing-lg);
  background-color: var(--color-bg-primary);
  color: var(--color-text-primary);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: 0.875rem;
  font-weight: 500;
  cursor: pointer;
  transition: all var(--transition-fast);
  min-height: 44px;
  min-width: 44px;
}

.pagination button:hover:not(:disabled) {
  background-color: var(--color-primary);
  color: var(--color-text-inverse);
  border-color: var(--color-primary);
}

.pagination button:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.pagination .page-info {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  padding: 0 var(--spacing-md);
}

/* ===================================
   Responsive Design
   =================================== */

/* Tablet (768px and below) */
@media (max-width: 768px) {
  .container {
    padding: 0 var(--spacing-sm);
  }
  
  .header {
    padding: var(--spacing-lg) 0;
  }
  
  .app-title {
    font-size: 1.5rem;
  }
  
  .app-subtitle {
    font-size: 0.875rem;
  }
  
  /* Stack search options vertically */
  .search-options {
    flex-direction: column;
  }
  
  .search-bar {
    flex-direction: column;
  }
  
  /* Stack filter panel vertically */
  .filter-panel {
    grid-template-columns: 1fr;
  }
  
  .filter-actions {
    flex-direction: column;
  }
  
  /* Reduce grid columns */
  .results-grid {
    grid-template-columns: repeat(2, 1fr);
    gap: var(--spacing-md);
  }
  
  .stats-grid {
    grid-template-columns: repeat(2, 1fr);
  }
  
  /* Book detail modal */
  .book-detail {
    grid-template-columns: 1fr;
  }
  
  .book-detail-sidebar {
    max-width: 250px;
    margin: 0 auto;
  }
  
  /* Comparison table scrollable */
  .comparison-table-wrapper {
    overflow-x: scroll;
    -webkit-overflow-scrolling: touch;
  }
  
  .comparison-table {
    min-width: 600px;
  }
  
  /* Controls section */
  .controls-section {
    flex-direction: column;
    align-items: stretch;
  }
  
  .export-controls {
    flex-direction: column;
    align-items: stretch;
  }
}

/* Mobile (480px and below) */
@media (max-width: 480px) {
  html {
    font-size: 14px;
  }
  
  .header {
    padding: var(--spacing-md) 0;
  }
  
  .app-title {
    font-size: 1.25rem;
  }
  
  .section-title {
    font-size: 1.25rem;
  }
  
  /* Single column layout */
  .results-grid {
    grid-template-columns: 1fr;
  }
  
  .stats-grid {
    grid-template-columns: 1fr;
  }
  
  .search-stats {
    grid-template-columns: 1fr;
  }
  
  /* Reduce padding */
  .search-section,
  .genre-section,
  .filter-section,
  .statistics-section,
  .controls-section {
    padding: var(--spacing-md);
  }
  
  .modal-content {
    width: 95%;
    padding: var(--spacing-md);
  }
  
  /* Smaller fonts */
  .book-title {
    font-size: 0.875rem;
  }
  
  .book-author {
    font-size: 0.75rem;
  }
  
  .book-meta {
    font-size: 0.625rem;
  }
  
  /* Ensure touch targets are at least 44x44px */
  .btn,
  .form-select,
  .form-input,
  .genre-btn,
  .btn-detail,
  .select-list {
    min-height: 44px;
    min-width: 44px;
  }
  
  /* Genre buttons full width on mobile */
  .genre-btn {
    flex: 1 1 calc(50% - var(--spacing-sm));
    min-width: 120px;
  }
  
  /* Pagination adjustments */
  .pagination {
    flex-wrap: wrap;
  }
}

/* Large Desktop (1200px and above) */
@media (min-width: 1200px) {
  .container {
    max-width: 1400px;
  }
  
  .results-grid {
    grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
  }
}