/* ============================================
   Japanese Books Tutor — Design System
   ============================================ */

/* --- Google Fonts --- */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&family=Noto+Sans+JP:wght@300;400;500;700&display=swap');

/* --- CSS Custom Properties --- */
:root {
  /* Color Palette — Deep indigo/navy with warm amber accents */
  --bg-primary: #0a0e1a;
  --bg-secondary: #111827;
  --bg-tertiary: #1a2236;
  --bg-card: rgba(26, 34, 54, 0.7);
  --bg-glass: rgba(26, 34, 54, 0.5);
  --bg-glass-hover: rgba(30, 40, 65, 0.7);
  --bg-input: rgba(15, 20, 35, 0.8);

  --border-subtle: rgba(255, 255, 255, 0.06);
  --border-medium: rgba(255, 255, 255, 0.1);
  --border-accent: rgba(245, 158, 11, 0.3);

  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --text-tertiary: #64748b;
  --text-accent: #f59e0b;
  --text-accent-light: #fbbf24;

  --accent-amber: #f59e0b;
  --accent-amber-glow: rgba(245, 158, 11, 0.15);
  --accent-amber-hover: #fbbf24;
  --accent-red: #ef4444;
  --accent-red-glow: rgba(239, 68, 68, 0.15);
  --accent-green: #22c55e;
  --accent-green-glow: rgba(34, 197, 94, 0.15);
  --accent-blue: #3b82f6;
  --accent-blue-glow: rgba(59, 130, 246, 0.15);
  --accent-purple: #a78bfa;

  /* Gradients */
  --gradient-amber: linear-gradient(135deg, #f59e0b, #d97706);
  --gradient-hero: linear-gradient(135deg, #f59e0b 0%, #ef4444 50%, #a78bfa 100%);
  --gradient-card: linear-gradient(145deg, rgba(26, 34, 54, 0.8), rgba(15, 20, 35, 0.6));
  --gradient-glass: linear-gradient(135deg, rgba(255,255,255,0.05), rgba(255,255,255,0.02));

  /* Shadows */
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.5);
  --shadow-glow-amber: 0 0 20px rgba(245, 158, 11, 0.2);
  --shadow-glow-blue: 0 0 20px rgba(59, 130, 246, 0.2);

  /* Typography */
  --font-ui: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  --font-jp: 'Noto Sans JP', 'Hiragino Sans', 'Yu Gothic', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Consolas', monospace;

  --text-xs: 0.75rem;
  --text-sm: 0.875rem;
  --text-base: 1rem;
  --text-lg: 1.125rem;
  --text-xl: 1.25rem;
  --text-2xl: 1.5rem;
  --text-3xl: 2rem;
  --text-4xl: 2.5rem;

  /* Spacing */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;

  /* Border Radius */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  --radius-full: 9999px;

  /* Transitions */
  --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-base: 250ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 400ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-spring: 500ms cubic-bezier(0.34, 1.56, 0.64, 1);

  /* Z-index scale */
  --z-dropdown: 100;
  --z-sticky: 200;
  --z-modal-backdrop: 300;
  --z-modal: 400;
  --z-toast: 500;
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-ui);
  background: var(--bg-primary);
  color: var(--text-primary);
  min-height: 100vh;
  line-height: 1.6;
  overflow-x: hidden;
}

/* Ambient background glow */
body::before {
  content: '';
  position: fixed;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background:
    radial-gradient(ellipse at 20% 20%, rgba(245, 158, 11, 0.04) 0%, transparent 50%),
    radial-gradient(ellipse at 80% 80%, rgba(59, 130, 246, 0.03) 0%, transparent 50%),
    radial-gradient(ellipse at 50% 50%, rgba(167, 139, 250, 0.02) 0%, transparent 50%);
  pointer-events: none;
  z-index: -1;
}

/* Japanese text */
.jp-text {
  font-family: var(--font-jp);
  line-height: 1.8;
}

/* --- Scrollbar --- */
::-webkit-scrollbar {
  width: 6px;
  height: 6px;
}

::-webkit-scrollbar-track {
  background: transparent;
}

::-webkit-scrollbar-thumb {
  background: rgba(255, 255, 255, 0.12);
  border-radius: var(--radius-full);
}

::-webkit-scrollbar-thumb:hover {
  background: rgba(255, 255, 255, 0.2);
}

/* --- Typography --- */
h1, h2, h3, h4 {
  font-weight: 600;
  line-height: 1.3;
  letter-spacing: -0.02em;
}

h1 { font-size: var(--text-4xl); }
h2 { font-size: var(--text-3xl); }
h3 { font-size: var(--text-2xl); }
h4 { font-size: var(--text-xl); }

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

a {
  color: var(--text-accent);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--text-accent-light);
}

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-3) var(--space-6);
  font-family: var(--font-ui);
  font-size: var(--text-sm);
  font-weight: 500;
  border: none;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--transition-base);
  white-space: nowrap;
  user-select: none;
  position: relative;
  overflow: hidden;
}

.btn::after {
  content: '';
  position: absolute;
  inset: 0;
  background: white;
  opacity: 0;
  transition: opacity var(--transition-fast);
}

.btn:hover::after {
  opacity: 0.05;
}

.btn:active {
  transform: scale(0.97);
}

.btn-primary {
  background: var(--gradient-amber);
  color: #0a0e1a;
  font-weight: 600;
  box-shadow: var(--shadow-glow-amber);
}

.btn-primary:hover {
  box-shadow: 0 0 30px rgba(245, 158, 11, 0.35);
  transform: translateY(-1px);
}

.btn-secondary {
  background: var(--bg-glass);
  color: var(--text-primary);
  border: 1px solid var(--border-medium);
  backdrop-filter: blur(12px);
}

.btn-secondary:hover {
  background: var(--bg-glass-hover);
  border-color: var(--border-accent);
}

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

.btn-ghost:hover {
  color: var(--text-primary);
  background: rgba(255, 255, 255, 0.05);
}

.btn-danger {
  background: rgba(239, 68, 68, 0.15);
  color: var(--accent-red);
  border: 1px solid rgba(239, 68, 68, 0.2);
}

.btn-danger:hover {
  background: rgba(239, 68, 68, 0.25);
}

.btn-sm {
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-xs);
}

.btn-lg {
  padding: var(--space-4) var(--space-8);
  font-size: var(--text-base);
  border-radius: var(--radius-lg);
}

.btn-icon {
  width: 40px;
  height: 40px;
  padding: 0;
  border-radius: var(--radius-md);
}

/* --- Cards --- */
.card {
  background: var(--gradient-card);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  backdrop-filter: blur(16px);
  transition: all var(--transition-base);
}

.card:hover {
  border-color: var(--border-medium);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.card-interactive {
  cursor: pointer;
}

.card-interactive:hover {
  border-color: var(--border-accent);
  box-shadow: var(--shadow-glow-amber);
}

/* --- Glass panels --- */
.glass {
  background: var(--bg-glass);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
}

/* --- Input fields --- */
.input {
  width: 100%;
  padding: var(--space-3) var(--space-4);
  background: var(--bg-input);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-family: var(--font-ui);
  font-size: var(--text-base);
  transition: all var(--transition-base);
  outline: none;
}

.input:focus {
  border-color: var(--accent-amber);
  box-shadow: 0 0 0 3px var(--accent-amber-glow);
}

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

textarea.input {
  resize: vertical;
  min-height: 80px;
}

/* --- Badge / Tag --- */
.badge {
  display: inline-flex;
  align-items: center;
  padding: var(--space-1) var(--space-3);
  font-size: var(--text-xs);
  font-weight: 600;
  border-radius: var(--radius-full);
  letter-spacing: 0.02em;
}

.badge-n5 {
  background: rgba(34, 197, 94, 0.15);
  color: #4ade80;
}

.badge-n4 {
  background: rgba(59, 130, 246, 0.15);
  color: #60a5fa;
}

.badge-n3 {
  background: rgba(245, 158, 11, 0.15);
  color: #fbbf24;
}

.badge-n2 {
  background: rgba(239, 68, 68, 0.15);
  color: #f87171;
}

.badge-n1 {
  background: rgba(167, 139, 250, 0.15);
  color: #c4b5fd;
}

/* --- Layout --- */
.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--space-6);
}

.container-narrow {
  max-width: 800px;
}

/* --- App Shell --- */
#app {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.app-header {
  position: sticky;
  top: 0;
  z-index: var(--z-sticky);
  padding: var(--space-4) var(--space-6);
  background: rgba(10, 14, 26, 0.85);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--border-subtle);
}

.app-header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: 1200px;
  margin: 0 auto;
}

.app-logo {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  font-size: var(--text-lg);
  font-weight: 700;
  color: var(--text-primary);
  cursor: pointer;
  transition: opacity var(--transition-fast);
}

.app-logo:hover {
  opacity: 0.85;
}

.app-logo-icon {
  font-size: var(--text-2xl);
}

.app-nav {
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

.app-main {
  flex: 1;
  padding: var(--space-8) var(--space-6);
}

/* --- View containers --- */
.view {
  display: none;
  animation: viewFadeIn 0.4s ease-out;
}

.view.active {
  display: block;
}

@keyframes viewFadeIn {
  from {
    opacity: 0;
    transform: translateY(12px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* --- Progress ring --- */
.progress-ring {
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.progress-ring svg {
  transform: rotate(-90deg);
}

.progress-ring-bg {
  stroke: rgba(255, 255, 255, 0.06);
}

.progress-ring-fill {
  stroke: var(--accent-amber);
  stroke-linecap: round;
  transition: stroke-dashoffset var(--transition-slow);
}

.progress-ring-text {
  position: absolute;
  font-size: var(--text-xs);
  font-weight: 600;
  color: var(--text-primary);
}

/* --- Modal --- */
.modal-backdrop {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.6);
  backdrop-filter: blur(4px);
  z-index: var(--z-modal-backdrop);
  opacity: 0;
  transition: opacity var(--transition-base);
  display: none;
}

.modal-backdrop.active {
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 1;
}

.modal {
  background: var(--bg-secondary);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-xl);
  padding: var(--space-8);
  max-width: 480px;
  width: 90%;
  max-height: 85vh;
  overflow-y: auto;
  z-index: var(--z-modal);
  animation: modalSlideIn 0.3s var(--transition-spring);
}

@keyframes modalSlideIn {
  from {
    opacity: 0;
    transform: scale(0.95) translateY(20px);
  }
  to {
    opacity: 1;
    transform: scale(1) translateY(0);
  }
}

.modal-title {
  font-size: var(--text-xl);
  margin-bottom: var(--space-4);
}

.modal-actions {
  display: flex;
  gap: var(--space-3);
  justify-content: flex-end;
  margin-top: var(--space-6);
}

/* --- Toast notifications --- */
.toast-container {
  position: fixed;
  bottom: var(--space-6);
  right: var(--space-6);
  z-index: var(--z-toast);
  display: flex;
  flex-direction: column-reverse;
  gap: var(--space-3);
}

.toast {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-4) var(--space-5);
  background: var(--bg-secondary);
  border: 1px solid var(--border-medium);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  font-size: var(--text-sm);
  min-width: 280px;
  max-width: 420px;
  animation: toastSlideIn 0.35s var(--transition-spring);
}

.toast.toast-exit {
  animation: toastSlideOut 0.25s ease-in forwards;
}

.toast-success {
  border-left: 3px solid var(--accent-green);
}

.toast-error {
  border-left: 3px solid var(--accent-red);
}

.toast-info {
  border-left: 3px solid var(--accent-blue);
}

@keyframes toastSlideIn {
  from {
    opacity: 0;
    transform: translateX(100%);
  }
  to {
    opacity: 1;
    transform: translateX(0);
  }
}

@keyframes toastSlideOut {
  to {
    opacity: 0;
    transform: translateX(100%);
  }
}

/* --- Drop Zone --- */
.drop-zone {
  position: relative;
  border: 2px dashed var(--border-medium);
  border-radius: var(--radius-xl);
  padding: var(--space-16);
  text-align: center;
  transition: all var(--transition-base);
  cursor: pointer;
  overflow: hidden;
}

.drop-zone::before {
  content: '';
  position: absolute;
  inset: 0;
  background: var(--accent-amber-glow);
  opacity: 0;
  transition: opacity var(--transition-base);
}

.drop-zone:hover,
.drop-zone.drag-over {
  border-color: var(--accent-amber);
  background: var(--accent-amber-glow);
}

.drop-zone:hover::before,
.drop-zone.drag-over::before {
  opacity: 1;
}

.drop-zone-icon {
  font-size: 3rem;
  margin-bottom: var(--space-4);
  opacity: 0.6;
  transition: all var(--transition-base);
}

.drop-zone:hover .drop-zone-icon,
.drop-zone.drag-over .drop-zone-icon {
  opacity: 1;
  transform: scale(1.1);
}

.drop-zone-text {
  font-size: var(--text-lg);
  color: var(--text-secondary);
  margin-bottom: var(--space-2);
}

.drop-zone-hint {
  font-size: var(--text-sm);
  color: var(--text-tertiary);
}

.drop-zone input[type="file"] {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  opacity: 0;
  cursor: pointer;
}

/* --- Processing overlay --- */
.processing-overlay {
  display: none;
  position: absolute;
  inset: 0;
  background: rgba(10, 14, 26, 0.9);
  backdrop-filter: blur(8px);
  border-radius: var(--radius-xl);
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: var(--space-4);
  z-index: 10;
}

.processing-overlay.active {
  display: flex;
}

.processing-spinner {
  width: 48px;
  height: 48px;
  border: 3px solid var(--border-medium);
  border-top-color: var(--accent-amber);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

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

.processing-text {
  font-size: var(--text-sm);
  color: var(--text-secondary);
}

/* --- Progress bar --- */
.progress-bar {
  width: 100%;
  height: 4px;
  background: rgba(255, 255, 255, 0.06);
  border-radius: var(--radius-full);
  overflow: hidden;
}

.progress-bar-fill {
  height: 100%;
  background: var(--gradient-amber);
  border-radius: var(--radius-full);
  transition: width var(--transition-base);
}

/* --- Empty state --- */
.empty-state {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: var(--space-16) var(--space-8);
  text-align: center;
}

.empty-state-icon {
  font-size: 4rem;
  margin-bottom: var(--space-6);
  opacity: 0.3;
}

.empty-state-title {
  font-size: var(--text-xl);
  font-weight: 600;
  margin-bottom: var(--space-3);
}

.empty-state-text {
  font-size: var(--text-sm);
  color: var(--text-tertiary);
  max-width: 400px;
  margin-bottom: var(--space-6);
}

/* --- Book grid --- */
.book-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: var(--space-6);
}

.book-card {
  padding: var(--space-6);
  position: relative;
}

.book-card-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  margin-bottom: var(--space-4);
}

.book-card-title {
  font-size: var(--text-lg);
  font-weight: 600;
  font-family: var(--font-jp);
  line-height: 1.4;
  flex: 1;
  margin-right: var(--space-3);
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.book-card-meta {
  display: flex;
  gap: var(--space-4);
  font-size: var(--text-sm);
  color: var(--text-tertiary);
  margin-bottom: var(--space-5);
}

.book-card-meta span {
  display: flex;
  align-items: center;
  gap: var(--space-1);
}

.book-card-progress {
  margin-bottom: var(--space-5);
}

.book-card-progress-label {
  display: flex;
  justify-content: space-between;
  font-size: var(--text-xs);
  color: var(--text-tertiary);
  margin-bottom: var(--space-2);
}

.book-card-actions {
  display: flex;
  gap: var(--space-3);
}

.book-card-delete {
  position: absolute;
  top: var(--space-4);
  right: var(--space-4);
  opacity: 0;
  transition: opacity var(--transition-fast);
}

.book-card:hover .book-card-delete {
  opacity: 1;
}

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

.text-amber { color: var(--text-accent); }
.text-muted { color: var(--text-tertiary); }
.text-center { text-align: center; }
.mt-2 { margin-top: var(--space-2); }
.mt-4 { margin-top: var(--space-4); }
.mt-6 { margin-top: var(--space-6); }
.mt-8 { margin-top: var(--space-8); }
.mb-4 { margin-bottom: var(--space-4); }
.mb-6 { margin-bottom: var(--space-6); }
.flex { display: flex; }
.flex-col { flex-direction: column; }
.items-center { align-items: center; }
.justify-between { justify-content: space-between; }
.gap-2 { gap: var(--space-2); }
.gap-3 { gap: var(--space-3); }
.gap-4 { gap: var(--space-4); }
.gap-6 { gap: var(--space-6); }

/* --- Responsive --- */
@media (max-width: 768px) {
  :root {
    --text-4xl: 2rem;
    --text-3xl: 1.5rem;
  }

  .app-header {
    padding: var(--space-3) var(--space-4);
  }

  .app-main {
    padding: var(--space-6) var(--space-4);
  }

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

  .drop-zone {
    padding: var(--space-10);
  }

  .container {
    padding: 0 var(--space-4);
  }
}

@media (max-width: 480px) {
  .modal {
    width: 95%;
    padding: var(--space-6);
  }

  .toast-container {
    left: var(--space-4);
    right: var(--space-4);
  }

  .toast {
    min-width: auto;
  }
}

/* --- Settings view --- */
.settings-section {
  margin-bottom: var(--space-8);
  padding-bottom: var(--space-8);
  border-bottom: 1px solid var(--border-subtle);
}

.settings-section:last-child {
  border-bottom: none;
}

.settings-section-title {
  font-size: var(--text-lg);
  font-weight: 600;
  margin-bottom: var(--space-2);
}

.settings-section-desc {
  font-size: var(--text-sm);
  color: var(--text-tertiary);
  margin-bottom: var(--space-4);
}

.settings-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
  padding: var(--space-4) 0;
}

.settings-row + .settings-row {
  border-top: 1px solid var(--border-subtle);
}

.settings-row-label {
  font-size: var(--text-sm);
  font-weight: 500;
}

.settings-row-desc {
  font-size: var(--text-xs);
  color: var(--text-tertiary);
  margin-top: var(--space-1);
}