/* ==========================================================================
   AI Flashcard Generator - Modern CSS Design System & Theme Variables
   Targeting Core Web Vitals (Zero CLS, High Contrast, Fluid Typography)
   ========================================================================== */

:root {
  /* Color Palette - Light Mode (Cool/Warm Balanced Neutrals) */
  --bg-primary: #f8fafc;
  --bg-surface: #ffffff;
  --bg-surface-subtle: #f1f5f9;
  --bg-surface-elevated: #ffffff;
  --border-subtle: #e2e8f0;
  --border-strong: #cbd5e1;
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #64748b;
  --text-inverse: #ffffff;

  /* Brand Accents */
  --brand-primary: #2563eb;
  --brand-primary-hover: #1d4ed8;
  --brand-primary-light: #eff6ff;
  --brand-accent: #0284c7;
  --brand-gradient: linear-gradient(135deg, #2563eb 0%, #0284c7 100%);
  
  /* Status Colors */
  --success: #10b981;
  --success-bg: #ecfdf5;
  --success-border: #a7f3d0;
  --warning: #f59e0b;
  --warning-bg: #fffbeb;
  --warning-border: #fde68a;
  --danger: #ef4444;
  --danger-bg: #fef2f2;
  --danger-border: #fecaca;
  --info: #3b82f6;

  /* Spacing & Radii */
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  --radius-full: 9999px;

  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 0 2px 4px -2px rgba(0, 0, 0, 0.05);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -4px rgba(0, 0, 0, 0.04);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.09), 0 8px 10px -6px rgba(0, 0, 0, 0.04);
  --shadow-card: 0 12px 30px -5px rgba(37, 99, 235, 0.08), 0 4px 10px -2px rgba(0, 0, 0, 0.04);

  /* Typography */
  --font-sans: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
  --transition-fast: 0.15s ease;
  --transition-normal: 0.25s ease;
  --container-max: 1200px;
}

[data-theme="dark"] {
  --bg-primary: #0b1120;
  --bg-surface: #131d31;
  --bg-surface-subtle: #1e293b;
  --bg-surface-elevated: #1e293b;
  --border-subtle: #1e293b;
  --border-strong: #334155;
  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  --text-inverse: #0f172a;

  --brand-primary: #3b82f6;
  --brand-primary-hover: #60a5fa;
  --brand-primary-light: rgba(59, 130, 246, 0.15);
  --brand-accent: #38bdf8;
  --brand-gradient: linear-gradient(135deg, #3b82f6 0%, #38bdf8 100%);

  --success: #34d399;
  --success-bg: rgba(16, 185, 129, 0.15);
  --success-border: rgba(16, 185, 129, 0.3);
  --warning: #fbbf24;
  --warning-bg: rgba(245, 158, 11, 0.15);
  --warning-border: rgba(245, 158, 11, 0.3);
  --danger: #f87171;
  --danger-bg: rgba(239, 68, 68, 0.15);
  --danger-border: rgba(239, 68, 68, 0.3);

  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.5);
  --shadow-card: 0 12px 30px -5px rgba(0, 0, 0, 0.6);
}

/* ==========================================================================
   Base Reset & Typography
   ========================================================================== */

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

html {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.6;
  color: var(--text-primary);
  background-color: var(--bg-primary);
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  color: var(--text-primary);
  background-color: var(--bg-primary);
  overflow-x: hidden;
}

img, svg {
  display: block;
  max-width: 100%;
  height: auto;
}

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

a:hover {
  color: var(--brand-primary-hover);
}

h1, h2, h3, h4, h5, h6 {
  color: var(--text-primary);
  font-weight: 700;
  line-height: 1.25;
  letter-spacing: -0.02em;
}

h1 { font-size: clamp(2rem, 4vw + 1rem, 3.25rem); }
h2 { font-size: clamp(1.5rem, 2.5vw + 0.5rem, 2.25rem); margin-top: 2rem; margin-bottom: 1rem; }
h3 { font-size: clamp(1.2rem, 1.5vw + 0.5rem, 1.5rem); margin-top: 1.5rem; margin-bottom: 0.75rem; }
p { margin-bottom: 1.25rem; color: var(--text-secondary); }

/* ==========================================================================
   Layout Containers & Grid
   ========================================================================== */

.container {
  width: 100%;
  max-width: var(--container-max);
  margin-left: auto;
  margin-right: auto;
  padding-left: 1.25rem;
  padding-right: 1.25rem;
}

.container-narrow {
  max-width: 860px;
}

.grid {
  display: grid;
  gap: 1.5rem;
}

.grid-cols-1 { grid-template-columns: repeat(1, minmax(0, 1fr)); }
.grid-cols-2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.grid-cols-3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
.grid-cols-4 { grid-template-columns: repeat(4, minmax(0, 1fr)); }

@media (max-width: 1024px) {
  .grid-cols-4 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .grid-cols-3 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (max-width: 768px) {
  .grid-cols-4, .grid-cols-3, .grid-cols-2 { grid-template-columns: 1fr; }
}

/* ==========================================================================
   Header & Navigation
   ========================================================================== */

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background-color: var(--bg-surface);
  border-bottom: 1px solid var(--border-subtle);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  transition: background-color var(--transition-normal);
}

.nav-container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 4.25rem;
}

.logo-link {
  display: flex;
  align-items: center;
  gap: 0.625rem;
  font-weight: 800;
  font-size: 1.25rem;
  color: var(--text-primary);
  text-decoration: none;
}

.logo-icon {
  width: 2rem;
  height: 2rem;
  background: var(--brand-gradient);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  color: #ffffff;
  font-weight: 900;
  box-shadow: 0 2px 8px rgba(37, 99, 235, 0.35);
}

.nav-right-group {
  display: flex;
  align-items: center;
  gap: 1.25rem;
}

.nav-menu {
  display: flex;
  align-items: center;
  gap: 1.25rem;
  list-style: none;
}

.nav-link {
  font-weight: 600;
  font-size: 0.9375rem;
  color: var(--text-secondary);
  transition: color var(--transition-fast);
  white-space: nowrap;
  padding: 0.375rem 0.25rem;
}

.nav-link:hover, .nav-link.active {
  color: var(--brand-primary);
}

.nav-actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.nav-cta-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.375rem;
  padding: 0.5rem 1rem;
  font-size: 0.875rem;
  font-weight: 700;
  border-radius: var(--radius-md);
  background: var(--brand-gradient);
  color: #ffffff !important;
  box-shadow: 0 2px 8px rgba(37, 99, 235, 0.35);
  transition: transform var(--transition-fast), box-shadow var(--transition-fast);
}

.nav-cta-btn:hover {
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(37, 99, 235, 0.45);
}

/* Mobile Navigation Drawer */
.mobile-menu-btn {
  display: none;
  background: none;
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  color: var(--text-primary);
  font-size: 1.25rem;
  cursor: pointer;
  padding: 0.375rem 0.625rem;
  line-height: 1;
}

@media (max-width: 960px) {
  .mobile-menu-btn { display: inline-flex; align-items: center; justify-content: center; }
  .nav-menu {
    display: none;
    position: fixed;
    top: 4.25rem;
    left: 0;
    width: 100%;
    background-color: var(--bg-surface);
    border-bottom: 1px solid var(--border-subtle);
    padding: 1.5rem;
    flex-direction: column;
    align-items: flex-start;
    gap: 1.25rem;
    box-shadow: var(--shadow-lg);
    z-index: 99;
  }
  .nav-menu.open { display: flex; }
  .nav-menu .mobile-only-cta { display: block; width: 100%; margin-top: 0.5rem; }
  .desktop-only-cta { display: none; }
}

@media (min-width: 961px) {
  .mobile-only-cta { display: none; }
}

/* ==========================================================================
   Buttons & Controls
   ========================================================================== */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.625rem 1.25rem;
  font-weight: 600;
  font-size: 0.9375rem;
  border-radius: var(--radius-md);
  border: 1px solid transparent;
  cursor: pointer;
  transition: all var(--transition-fast);
  text-align: center;
  text-decoration: none;
  white-space: nowrap;
  line-height: 1.2;
}

.btn:active {
  transform: scale(0.98);
}

.btn-primary {
  background-color: var(--brand-primary);
  color: #ffffff;
  box-shadow: 0 2px 4px rgba(37, 99, 235, 0.2);
}

.btn-primary:hover {
  background-color: var(--brand-primary-hover);
  color: #ffffff;
}

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

.btn-secondary:hover {
  background-color: var(--bg-surface-subtle);
  border-color: var(--brand-primary);
}

.btn-success {
  background-color: var(--success);
  color: #ffffff;
}

.btn-danger {
  background-color: var(--danger);
  color: #ffffff;
}

.btn-sm {
  padding: 0.375rem 0.75rem;
  font-size: 0.8125rem;
}

.btn-lg {
  padding: 0.875rem 1.75rem;
  font-size: 1.0625rem;
  border-radius: var(--radius-lg);
}

.theme-toggle {
  background: none;
  border: 1px solid var(--border-subtle);
  color: var(--text-secondary);
  border-radius: var(--radius-md);
  padding: 0.5rem 0.625rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
}

.theme-toggle:hover {
  background-color: var(--bg-surface-subtle);
  color: var(--text-primary);
}

/* ==========================================================================
   Tool Section & Generator UI
   ========================================================================== */

.hero-section {
  padding: 3rem 0 2rem;
  text-align: center;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.35rem 0.85rem;
  border-radius: var(--radius-full);
  background-color: var(--brand-primary-light);
  color: var(--brand-primary);
  font-size: 0.875rem;
  font-weight: 700;
  margin-bottom: 1.25rem;
  border: 1px solid rgba(37, 99, 235, 0.2);
}

.hero-title {
  margin-bottom: 1rem;
}

.hero-subtitle {
  font-size: 1.1875rem;
  max-width: 720px;
  margin: 0 auto 2.5rem;
  color: var(--text-secondary);
}

.tool-card {
  background-color: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow-card);
  padding: 2rem;
  margin-bottom: 3rem;
  position: relative;
}

@media (max-width: 768px) {
  .tool-card { padding: 1.25rem; }
}

/* Tab Navigation */
.tabs-container {
  display: flex;
  gap: 0.5rem;
  border-bottom: 1px solid var(--border-subtle);
  padding-bottom: 1rem;
  margin-bottom: 1.5rem;
  overflow-x: auto;
}

.tab-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.625rem 1.25rem;
  border-radius: var(--radius-md);
  border: none;
  background-color: transparent;
  color: var(--text-secondary);
  font-weight: 600;
  font-size: 0.9375rem;
  cursor: pointer;
  transition: all var(--transition-fast);
  white-space: nowrap;
}

.tab-btn:hover {
  background-color: var(--bg-surface-subtle);
  color: var(--text-primary);
}

.tab-btn.active {
  background-color: var(--brand-primary);
  color: #ffffff;
}

/* Forms & Textarea */
.form-group {
  margin-bottom: 1.25rem;
  text-align: left;
}

.form-label {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-weight: 600;
  font-size: 0.875rem;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.form-control {
  width: 100%;
  padding: 0.875rem 1rem;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-md);
  background-color: var(--bg-surface);
  color: var(--text-primary);
  font-family: inherit;
  font-size: 0.9375rem;
  line-height: 1.5;
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.form-control:focus {
  outline: none;
  border-color: var(--brand-primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}

textarea.form-control {
  resize: vertical;
  min-height: 140px;
}

.form-helper {
  display: flex;
  justify-content: space-between;
  font-size: 0.8125rem;
  color: var(--text-muted);
  margin-top: 0.375rem;
}

.sample-pills {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: 0.5rem;
}

.sample-pill {
  font-size: 0.75rem;
  padding: 0.25rem 0.625rem;
  background-color: var(--bg-surface-subtle);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-full);
  color: var(--text-secondary);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.sample-pill:hover {
  background-color: var(--brand-primary-light);
  color: var(--brand-primary);
  border-color: var(--brand-primary);
}

.settings-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.api-key-accordion {
  margin-top: 1rem;
  margin-bottom: 1.5rem;
  border: 1px dashed var(--border-strong);
  border-radius: var(--radius-md);
  padding: 0.75rem 1rem;
  background-color: var(--bg-surface-subtle);
  text-align: left;
}

.api-key-toggle {
  display: flex;
  align-items: center;
  justify-content: space-between;
  cursor: pointer;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-secondary);
}

/* Generator Loading Bar */
.generator-loading {
  display: none;
  margin: 1.5rem 0;
  text-align: center;
}

.loading-bar {
  height: 6px;
  width: 100%;
  background-color: var(--bg-surface-subtle);
  border-radius: var(--radius-full);
  overflow: hidden;
  position: relative;
  margin-bottom: 0.75rem;
}

.loading-bar-inner {
  height: 100%;
  width: 30%;
  background: var(--brand-gradient);
  border-radius: var(--radius-full);
  animation: loadingAnim 1.4s infinite ease-in-out;
}

@keyframes loadingAnim {
  0% { transform: translateX(-100%); width: 20%; }
  50% { width: 60%; }
  100% { transform: translateX(200%); width: 20%; }
}

/* ==========================================================================
   Flashcards Interactive Workspace (Study Mode + Deck View)
   ========================================================================== */

.flashcard-workspace {
  display: none;
  margin-top: 2rem;
  border-top: 1px solid var(--border-subtle);
  padding-top: 2rem;
  text-align: left;
}

.workspace-header {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.deck-title-wrapper h3 {
  margin: 0;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.deck-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

/* 3D Flip Card Container */
.study-mode-container {
  max-width: 680px;
  margin: 0 auto 2rem;
  perspective: 1200px;
}

.flip-card {
  width: 100%;
  min-height: 320px;
  height: auto;
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
  cursor: pointer;
  border-radius: var(--radius-xl);
}

.flip-card.flipped {
  transform: rotateY(180deg);
}

.card-face {
  position: relative;
  width: 100%;
  min-height: 320px;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  border-radius: var(--radius-xl);
  padding: 2.25rem 2rem;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  background-color: var(--bg-surface);
  border: 2px solid var(--border-subtle);
  box-shadow: var(--shadow-lg);
  user-select: none;
}

.card-face.card-back {
  transform: rotateY(180deg);
  background-color: var(--bg-surface-elevated);
  border-color: var(--brand-primary);
}

.card-header-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1rem;
}

.card-type-tag {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  padding: 0.25rem 0.625rem;
  border-radius: var(--radius-full);
  background-color: var(--bg-surface-subtle);
  color: var(--text-secondary);
}

.card-audio-btn {
  background: none;
  border: none;
  color: var(--brand-primary);
  font-size: 1.25rem;
  cursor: pointer;
  padding: 0.35rem;
  border-radius: var(--radius-md);
  transition: transform var(--transition-fast);
}

.card-audio-btn:hover {
  transform: scale(1.15);
}

.card-body-text {
  font-size: 1.35rem;
  font-weight: 600;
  line-height: 1.5;
  color: var(--text-primary);
  margin: auto 0;
  text-align: center;
}

.card-footer-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.8125rem;
  color: var(--text-muted);
  margin-top: 1rem;
}

.card-hint {
  font-size: 0.875rem;
  color: var(--brand-accent);
  font-style: italic;
  margin-top: 0.5rem;
  text-align: center;
}

/* Study Controls */
.study-controls {
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
  align-items: center;
}

.study-progress-bar {
  width: 100%;
  max-width: 680px;
  height: 8px;
  background-color: var(--bg-surface-subtle);
  border-radius: var(--radius-full);
  overflow: hidden;
}

.study-progress-fill {
  height: 100%;
  width: 0%;
  background: var(--brand-gradient);
  transition: width 0.3s ease;
}

.study-rating-buttons {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
  justify-content: center;
}

.btn-leitner-1 {
  background-color: var(--danger-bg);
  color: var(--danger);
  border: 1px solid var(--danger-border);
}
.btn-leitner-1:hover { background-color: var(--danger); color: #fff; }

.btn-leitner-2 {
  background-color: var(--warning-bg);
  color: var(--warning);
  border: 1px solid var(--warning-border);
}
.btn-leitner-2:hover { background-color: var(--warning); color: #fff; }

.btn-leitner-3 {
  background-color: var(--success-bg);
  color: var(--success);
  border: 1px solid var(--success-border);
}
.btn-leitner-3:hover { background-color: var(--success); color: #fff; }

.keyboard-hint {
  font-size: 0.8125rem;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 0.75rem;
  flex-wrap: wrap;
  justify-content: center;
}

.kbd {
  background-color: var(--bg-surface-subtle);
  border: 1px solid var(--border-strong);
  border-radius: 4px;
  padding: 0.15rem 0.4rem;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  box-shadow: 0 1px 1px rgba(0,0,0,0.1);
}

/* Deck Grid View (Edit & Browse) */
.deck-grid-view {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 1.25rem;
  margin-top: 2rem;
}

.deck-item-card {
  background-color: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 1.25rem;
  box-shadow: var(--shadow-sm);
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  position: relative;
  transition: transform var(--transition-fast), border-color var(--transition-fast);
}

.deck-item-card:hover {
  border-color: var(--brand-primary);
  transform: translateY(-2px);
}

.deck-item-front {
  font-weight: 700;
  font-size: 1rem;
  color: var(--text-primary);
  margin-bottom: 0.75rem;
}

.deck-item-back {
  font-size: 0.9375rem;
  color: var(--text-secondary);
  border-top: 1px dashed var(--border-subtle);
  padding-top: 0.75rem;
  margin-bottom: 1rem;
}

.deck-item-controls {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.8125rem;
  color: var(--text-muted);
}

.leitner-badge {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.2rem 0.5rem;
  border-radius: var(--radius-full);
  font-size: 0.75rem;
  font-weight: 700;
}

.leitner-box-1 { background-color: var(--danger-bg); color: var(--danger); }
.leitner-box-2 { background-color: var(--warning-bg); color: var(--warning); }
.leitner-box-3 { background-color: var(--success-bg); color: var(--success); }

/* ==========================================================================
   Content & Editorial Sections (SEO & Knowledge Hub)
   ========================================================================== */

.content-section {
  padding: 4rem 0;
  border-top: 1px solid var(--border-subtle);
}

.prose {
  line-height: 1.75;
  font-size: 1.0625rem;
}

.prose h2 {
  font-size: 1.875rem;
  margin-top: 2.5rem;
  margin-bottom: 1.25rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--border-subtle);
}

.prose h3 {
  font-size: 1.375rem;
  margin-top: 2rem;
  margin-bottom: 0.75rem;
  color: var(--brand-primary);
}

.prose ul, .prose ol {
  margin-bottom: 1.5rem;
  padding-left: 1.5rem;
}

.prose li {
  margin-bottom: 0.5rem;
  color: var(--text-secondary);
}

.prose blockquote {
  border-left: 4px solid var(--brand-primary);
  padding: 0.75rem 1.25rem;
  margin: 1.5rem 0;
  background-color: var(--bg-surface-subtle);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  font-style: italic;
  color: var(--text-primary);
}

/* Feature Cards Grid */
.feature-card {
  background-color: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition-normal), box-shadow var(--transition-normal);
}

.feature-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
  border-color: var(--brand-primary);
}

.feature-icon-wrapper {
  width: 3rem;
  height: 3rem;
  background: var(--brand-primary-light);
  color: var(--brand-primary);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  margin-bottom: 1.25rem;
}

/* Comparison Table */
.table-responsive {
  overflow-x: auto;
  margin: 2rem 0;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-sm);
}

.comparison-table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
  background-color: var(--bg-surface);
}

.comparison-table th, .comparison-table td {
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--border-subtle);
}

.comparison-table th {
  background-color: var(--bg-surface-subtle);
  font-weight: 700;
  color: var(--text-primary);
  font-size: 0.9375rem;
}

.comparison-table tr:last-child td {
  border-bottom: none;
}

.comparison-table tr:hover td {
  background-color: var(--bg-surface-subtle);
}

/* FAQ Accordion */
.faq-list {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  margin: 2rem 0;
}

.faq-item {
  background-color: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  overflow: hidden;
  transition: border-color var(--transition-fast);
}

.faq-item:hover {
  border-color: var(--border-strong);
}

.faq-question {
  width: 100%;
  padding: 1.25rem 1.5rem;
  background: none;
  border: none;
  text-align: left;
  font-weight: 700;
  font-size: 1.0625rem;
  color: var(--text-primary);
  display: flex;
  justify-content: space-between;
  align-items: center;
  cursor: pointer;
}

.faq-icon {
  font-size: 1.25rem;
  transition: transform var(--transition-fast);
  color: var(--brand-primary);
}

.faq-item.open .faq-icon {
  transform: rotate(180deg);
}

.faq-answer {
  display: none;
  padding: 0 1.5rem 1.25rem;
  color: var(--text-secondary);
  line-height: 1.7;
}

.faq-item.open .faq-answer {
  display: block;
}

/* ==========================================================================
   Footer & Global Utility
   ========================================================================== */

.site-footer {
  background-color: var(--bg-surface);
  border-top: 1px solid var(--border-subtle);
  padding: 4rem 0 2rem;
  margin-top: auto;
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: 2.5rem;
  margin-bottom: 3rem;
}

@media (max-width: 880px) {
  .footer-grid { grid-template-columns: 1fr 1fr; }
}

@media (max-width: 520px) {
  .footer-grid { grid-template-columns: 1fr; }
}

.footer-column h4 {
  font-size: 1rem;
  font-weight: 700;
  margin-bottom: 1.25rem;
  color: var(--text-primary);
}

.footer-links {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
}

.footer-links a {
  color: var(--text-secondary);
  font-size: 0.9375rem;
}

.footer-links a:hover {
  color: var(--brand-primary);
}

.footer-bottom {
  padding-top: 2rem;
  border-top: 1px solid var(--border-subtle);
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  font-size: 0.875rem;
  color: var(--text-muted);
}

/* Toast Notifications */
.toast-container {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  z-index: 100;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.toast {
  background-color: var(--text-primary);
  color: var(--bg-primary);
  padding: 0.75rem 1.25rem;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
  font-size: 0.875rem;
  font-weight: 600;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  animation: toastSlideIn 0.3s ease;
}

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

/* Modal Popup */
.modal-overlay {
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.6);
  z-index: 99;
  backdrop-filter: blur(4px);
  align-items: center;
  justify-content: center;
  padding: 1rem;
}

.modal-overlay.open {
  display: flex;
}

.modal-content {
  background-color: var(--bg-surface);
  border-radius: var(--radius-xl);
  max-width: 540px;
  width: 100%;
  padding: 2rem;
  box-shadow: var(--shadow-xl);
  border: 1px solid var(--border-subtle);
  position: relative;
  text-align: left;
}

.modal-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1.25rem;
}

.modal-close {
  background: none;
  border: none;
  font-size: 1.5rem;
  cursor: pointer;
  color: var(--text-muted);
}

/* ==========================================================================
   Print Stylesheet for Clean Flashcard Printing & PDF Export
   ========================================================================== */

@media print {
  body {
    background: #ffffff !important;
    color: #000000 !important;
  }

  .site-header, .site-footer, .hero-section, .tabs-container, .settings-grid,
  .deck-actions, .study-mode-container, .content-section, .toast-container {
    display: none !important;
  }

  .flashcard-workspace {
    display: block !important;
    border: none !important;
    padding: 0 !important;
  }

  .deck-grid-view {
    display: grid !important;
    grid-template-columns: repeat(2, 1fr) !important;
    gap: 1.5cm !important;
    page-break-inside: avoid;
  }

  .deck-item-card {
    border: 2px solid #000000 !important;
    box-shadow: none !important;
    padding: 1.5cm !important;
    min-height: 8cm !important;
    page-break-inside: avoid;
  }

  .deck-item-front {
    font-size: 14pt !important;
    color: #000000 !important;
  }

  .deck-item-back {
    font-size: 12pt !important;
    color: #333333 !important;
    border-top: 1px solid #000000 !important;
  }
}