/* ========================================
   BMW Flashcard App - CSS Custom Properties
   Light Mode Theme
   ======================================== */

/* ========================================
   1. CSS CUSTOM PROPERTIES (Variables)
   ======================================== */

:root {
  /* ---- Colors - BMW Branding ---- */
  --color-primary: #1e40af;
  --color-primary-dark: #1e3a8a;
  --color-primary-light: #3b82f6;
  --color-accent: #dc2626;

  /* ---- Backgrounds ---- */
  --bg-primary: #ffffff;
  --bg-secondary: #f9fafb;
  --bg-tertiary: #f3f4f6;

  /* ---- Text Colors ---- */
  --text-primary: #1f2937;
  --text-secondary: #6b7280;
  --text-tertiary: #9ca3af;
  --text-inverse: #ffffff;

  /* ---- Borders ---- */
  --border-color: #e5e7eb;
  --border-light: #f3f4f6;

  /* ---- 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 -2px rgba(0, 0, 0, 0.1);
  --shadow-lg:
    0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -4px rgba(0, 0, 0, 0.1);
  --shadow-xl:
    0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 8px 10px -6px rgba(0, 0, 0, 0.1);

  /* ---- Spacing Scale ---- */
  --space-xs: 0.5rem;
  --space-sm: 1rem;
  --space-md: 1.5rem;
  --space-lg: 2rem;
  --space-xl: 3rem;

  /* ---- Typography ---- */
  --font-family:
    -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue",
    Arial, sans-serif;
  --font-mono: "Monaco", "Menlo", "Courier New", monospace;

  --font-size-sm: 0.875rem;
  --font-size-base: 1rem;
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.875rem;
  --font-size-base: 1rem;

  /* ---- Transitions ---- */
  --transition-fast: all 150ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-base: all 250ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: all 350ms cubic-bezier(0.4, 0, 0.2, 1);
}

/* Dark Mode Theme */
[data-theme="dark"] {
  /* ---- Colors - Dark Theme ---- */
  --color-primary: #3b82f6;
  --color-primary-dark: #60a5fa;
  --color-primary-light: #93c5fd;
  --color-accent: #f87171;

  /* ---- Backgrounds - Dark Navy ---- */
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-tertiary: #334155;

  /* ---- Text Colors - Light ---- */
  --text-primary: #f1f5f9;
  --text-secondary: #cbd5e1;
  --text-tertiary: #94a3b8;
  --text-inverse: #0f172a;

  /* ---- Borders - Dark Gray ---- */
  --border-color: #475569;
  --border-light: #334155;

  /* ---- Shadows - Higher Opacity ---- */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
  --shadow-md:
    0 4px 6px -1px rgba(0, 0, 0, 0.3), 0 2px 4px -2px rgba(0, 0, 0, 0.3);
  --shadow-lg:
    0 10px 15px -3px rgba(0, 0, 0, 0.3), 0 4px 6px -4px rgba(0, 0, 0, 0.3);
  --shadow-xl:
    0 20px 25px -5px rgba(0, 0, 0, 0.3), 0 8px 10px -6px rgba(0, 0, 0, 0.3);
}

/* ========================================
   2. GLOBAL RESET & BASE STYLES
   ======================================== */

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

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  line-height: 1.6;
  color: var(--text-primary);
  background-color: var(--bg-primary);
  transition:
    background-color var(--transition-base),
    color var(--transition-base);
}

/* ========================================
   3. UTILITY CLASSES
   ======================================== */

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

/* ========================================
   4. NAVIGATION BAR & THEME TOGGLE
   ======================================== */

nav {
  position: sticky;
  top: 0;
  background-color: var(--bg-secondary);
  border-bottom: 2px solid var(--border-color);
  padding: var(--space-md) var(--space-lg);
  z-index: 100;
  box-shadow: var(--shadow-md);
  transition: var(--transition-base);
}

nav header {
  width: 100%;
  padding: 0;
}

.nav-container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  max-width: 1200px;
  margin: 0 auto;
  gap: var(--space-lg);
}

.logo-section {
  display: flex;
  flex-direction: column;
  gap: var(--space-xs);
  flex: 1;
}

.logo-section .app-title {
  font-size: var(--font-size-xl);
  font-weight: 700;
  color: var(--color-primary);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  margin: 0;
}

.app-subtitle {
  font-size: var(--font-size-sm);
  font-weight: 400;
  color: var(--text-secondary);
  opacity: 0.75;
  margin: 0;
}

.nav-controls {
  display: flex;
  align-items: center;
  gap: var(--space-md);
}

#themeToggle {
  background-color: var(--bg-tertiary);
  border: 2px solid var(--border-color);
  width: 48px;
  height: 48px;
  border-radius: 0.5rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.25rem;
  transition: var(--transition-fast);
  flex-shrink: 0;
  padding: 0;
}

#themeToggle:hover {
  background-color: var(--color-primary-light);
  color: var(--text-inverse);
  transform: scale(1.05);
}

#themeToggle:active {
  transform: scale(0.95);
}

#themeToggle:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
}

.theme-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

/* Responsive Navigation */
@media (max-width: 768px) {
  nav {
    padding: var(--space-md) var(--space-sm);
  }

  .nav-container {
    gap: var(--space-md);
  }

  .logo-section .app-title {
    font-size: var(--font-size-lg);
  }

  .app-subtitle {
    display: none;
  }

  #themeToggle {
    width: 44px;
    height: 44px;
  }
}

@media (max-width: 480px) {
  nav {
    padding: var(--space-sm) var(--space-md);
  }

  .nav-container {
    gap: var(--space-sm);
  }

  .logo-section .app-title {
    font-size: var(--font-size-base);
  }

  #themeToggle {
    width: 40px;
    height: 40px;
    font-size: 1rem;
  }
}

/* ========================================
   5. MAIN CONTAINER
   ======================================== */

.main-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--space-lg) var(--space-md);
}

.app-section {
  background-color: var(--bg-primary);
  border-radius: 0.75rem;
  box-shadow: var(--shadow-md);
  padding: var(--space-lg);
  gap: var(--space-xl);
}

/* ========================================
   6. STATS BAR
   ======================================== */

/* Stats Bar - CSS Grid Layout */
.stats-bar {
  display: grid;
  grid-template-columns: 1fr auto 1fr auto 2fr;
  align-items: center;
  gap: var(--space-md);
  padding: var(--space-md);
  background-color: var(--bg-secondary);
  border-radius: 1rem;
  border: 2px solid var(--border-color);
  box-shadow: var(--shadow-md);
  margin-bottom: var(--space-xl);
}

.stat-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: var(--space-xs);
}

.stat-label {
  font-size: var(--font-size-sm);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-secondary);
}

.stat-value {
  font-size: var(--font-size-2xl);
  font-weight: 700;
  color: var(--color-primary);
}

.stat-divider {
  width: 2px;
  height: 40px;
  background-color: var(--border-color);
}

.progress-bar {
  width: 100px;
  height: 6px;
  background-color: var(--border-color);
  border-radius: 9999px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(
    90deg,
    var(--color-primary),
    var(--color-primary-light)
  );
  border-radius: 9999px;
  transition: width 0.3s ease;
}

/* ========================================
   7. FLASHCARD DISPLAY
   ======================================== */

.flashcard-section {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 400px;
}

.card-container {
  width: 100%;
  max-width: 600px;
  perspective: 1000px;
}

.flashcard {
  position: relative;
  max-width: 600px;
  height: 350px;
  width: 100%;
  cursor: pointer;
  perspective: 1000px;
  transform-style: preserve-3d;
  transition: var(--transition-slow);
}

.flashcard:hover {
  transform: translateY(-4px);
}

.card-front,
.card-back {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: var(--space-lg);
  border-radius: 1.25rem;
  box-shadow: var(--shadow-lg);
  text-align: center;
  transition:
    opacity var(--transition-base),
    transform var(--transition-base);
}

.card-front {
  background: linear-gradient(
    135deg,
    var(--color-primary),
    var(--color-primary-light)
  );
  color: var(--text-inverse);
  opacity: 1;
  transform: rotateY(0deg);
}

.card-back {
  background: linear-gradient(135deg, var(--color-accent), #f87171);
  color: var(--text-inverse);
  opacity: 0;
  transform: rotateY(180deg);
}

.card-front h2 {
  font-size: var(--font-size-2xl);
  margin-bottom: var(--space-md);
  line-height: 1.3;
}

.card-hint {
  font-size: var(--font-size-sm);
  opacity: 0.85;
  margin: 0;
  font-style: italic;
}

.card-back p {
  font-size: 2.5rem;
  font-weight: 700;
  margin: 0;
  line-height: 1.3;
}

/* ========================================
   8. STATUS MESSAGE
   ======================================== */

#statusMessage {
  min-height: 24px;
  padding: var(--space-md);
  text-align: center;
  font-size: var(--font-size-sm);
  color: var(--color-primary);
  font-weight: 500;
  transition: color var(--transition-base);
}

#statusMessage.success {
  color: #059669;
}

#statusMessage.error {
  color: var(--color-accent);
}

/* ========================================
   9. CONTROLS SECTION
   ======================================== */

.controls-section {
  display: flex;
  flex-direction: column;
  gap: var(--space-lg);
  padding-top: var(--space-lg);
  border-top: 1px solid var(--border-color);
}

.controls-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: var(--space-md);
  justify-items: stretch;
}

.nav-buttons {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-md);
  max-width: 400px;
  margin: 0 auto;
}

/* ========================================
   10. BUTTONS
   ======================================== */

.btn {
  padding: var(--space-sm) var(--space-md);
  border: 2px solid transparent;
  border-radius: 0.5rem;
  font-size: var(--font-size-sm);
  font-weight: 600;
  font-family: var(--font-family);
  cursor: pointer;
  transition: var(--transition-fast);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm);
  user-select: none;
  line-height: 1.4;
  min-height: 44px;
  min-width: 44px;
}

.btn:hover:not(:disabled) {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.btn:active:not(:disabled) {
  transform: translateY(0);
}

.btn:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
}

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

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

.btn-primary:hover:not(:disabled) {
  background-color: var(--color-primary-dark);
  border-color: var(--color-primary-dark);
}

.btn-primary:active:not(:disabled) {
  background-color: var(--color-primary-dark);
}

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

.btn-secondary:hover:not(:disabled) {
  background-color: var(--bg-tertiary);
  border-color: var(--color-primary-light);
}

.btn-secondary:active:not(:disabled) {
  background-color: var(--bg-tertiary);
}

.btn-nav {
  background-color: var(--bg-secondary);
  color: var(--text-primary);
  border-color: var(--border-color);
  font-size: var(--font-size-base);
  font-weight: 500;
}

.btn-nav:hover:not(:disabled) {
  background-color: var(--color-primary-light);
  color: var(--text-inverse);
  border-color: var(--color-primary-light);
}

.btn-nav:active:not(:disabled) {
  background-color: var(--color-primary-dark);
}

.btn-prev,
.btn-next {
  flex: 1;
}

/* ========================================
   11. CATEGORY SECTION
   ======================================== */

.category-section {
  padding: var(--space-lg) 0;
  border-top: 2px solid var(--border-color);
}

.category-section h2 {
  font-size: var(--font-size-2xl);
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: var(--space-lg);
  text-align: center;
}

.category-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: var(--space-md);
  margin-bottom: var(--space-xl);
}

.category-btn {
  padding: var(--space-md) var(--space-lg);
  border: 2px solid var(--border-color);
  border-radius: 0.75rem;
  background-color: var(--bg-secondary);
  color: var(--text-primary);
  font-size: var(--font-size-base);
  font-weight: 600;
  font-family: var(--font-family);
  cursor: pointer;
  transition: var(--transition-base);
  min-height: 50px;
}

.category-btn:hover {
  border-color: var(--color-primary-light);
  background-color: var(--bg-tertiary);
  transform: translateY(-2px);
}

.category-btn:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
}

.category-btn.active {
  background: linear-gradient(
    135deg,
    var(--color-primary),
    var(--color-primary-light)
  );
  color: var(--text-inverse);
  border-color: var(--color-primary);
  font-weight: 700;
  box-shadow: var(--shadow-lg);
}

.category-btn.active:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-xl);
}

/* ========================================
   12. INFO SECTION
   ======================================== */

.info-section {
  padding: var(--space-xl) 0;
  border-top: 2px solid var(--border-color);
}

.info-section h2 {
  font-size: var(--font-size-2xl);
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: var(--space-lg);
  text-align: center;
}

.info-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: var(--space-lg);
}

.info-card {
  background-color: var(--bg-secondary);
  border-radius: 0.75rem;
  padding: var(--space-lg);
  border-left: 4px solid var(--color-primary);
  transition: var(--transition-base);
}

.info-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
  border-left-color: var(--color-accent);
}

.info-card h3 {
  font-size: var(--font-size-lg);
  font-weight: 700;
  color: var(--color-primary);
  margin-bottom: var(--space-md);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.info-card p {
  font-size: var(--font-size-sm);
  color: var(--text-secondary);
  line-height: 1.6;
  margin: 0;
}

/* ========================================
   13. FOOTER
   ======================================== */

.app-footer {
  background-color: var(--bg-secondary);
  border-top: 1px solid var(--border-color);
  padding: var(--space-lg) var(--space-md);
  margin-top: var(--space-xl);
  font-size: var(--font-size-sm);
}

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

.instructions {
  color: var(--text-secondary);
  display: flex;
  gap: var(--space-lg);
  flex-wrap: wrap;
  align-items: center;
}

.instructions strong {
  font-weight: 600;
  color: var(--text-primary);
}

.shortcut {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
}

kbd {
  background-color: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  border-radius: 0.25rem;
  padding: var(--space-xs) var(--space-sm);
  font-family: var(--font-mono);
  font-size: var(--font-size-sm);
  color: var(--text-primary);
  font-weight: 500;
  box-shadow: var(--shadow-sm);
}

/* ========================================
   14. RESPONSIVE DESIGN
   ======================================== */

@media (max-width: 768px) {
  .nav-container {
    gap: var(--space-md);
  }

  .controls-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .category-grid {
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: var(--space-sm);
  }

  .category-btn {
    padding: var(--space-sm) var(--space-md);
    font-size: var(--font-size-sm);
    min-height: 45px;
  }

  .card-front,
  .card-back {
    padding: var(--space-lg);
    height: 300px;
  }

  .card-front h2 {
    font-size: var(--font-size-lg);
  }

  .card-back p {
    font-size: var(--font-size-2xl);
  }

  .flashcard-section {
    min-height: 320px;
  }
}

@media (max-width: 480px) {
  .main-container {
    padding: var(--space-md) var(--space-sm);
  }

  .app-section {
    padding: var(--space-md);
  }

  .stats-bar {
    flex-direction: column;
    gap: var(--space-sm);
    padding: var(--space-md);
  }

  .stat-divider {
    display: none;
  }

  .controls-grid {
    grid-template-columns: 1fr;
  }

  .category-grid {
    grid-template-columns: repeat(2, 1fr);
    gap: var(--space-sm);
  }

  .category-btn {
    padding: var(--space-sm) var(--space-xs);
    font-size: var(--font-size-sm);
    min-height: 40px;
  }

  .card-front,
  .card-back {
    padding: var(--space-md);
    height: 250px;
  }

  .card-front h2 {
    font-size: var(--font-size-lg);
  }

  .card-hint {
    font-size: var(--font-size-xs);
  }

  .card-back p {
    font-size: var(--font-size-xl);
  }

  .flashcard-section {
    min-height: 270px;
  }

  .info-grid {
    grid-template-columns: 1fr;
    gap: var(--space-md);
  }

  .info-card {
    padding: var(--space-md);
  }

  .info-card h3 {
    font-size: var(--font-size-base);
  }

  .info-card p {
    font-size: var(--font-size-xs);
  }
}

/* Flipped state animations */
.flashcard.flipped .card-front {
  opacity: 0;
  transform: rotateY(180deg);
}

.flashcard.flipped .card-back {
  opacity: 1;
  transform: rotateY(0deg);
}

/* Card title and answer styles */
.card-title {
  font-size: var(--font-size-2xl);
  font-weight: 700;
  margin-bottom: var(--space-md);
  line-height: 1.3;
}

.card-answer {
  font-size: var(--font-size-xl);
  font-weight: 600;
  line-height: 1.4;
}