:root {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-tertiary: #334155;
  --accent-cyan: #06b6d4;
  --accent-cyan-glow: rgba(6, 182, 212, 0.25);
  --accent-emerald: #10b981;
  --accent-emerald-glow: rgba(16, 185, 129, 0.25);
  --accent-rose: #f43f5e;
  --accent-rose-glow: rgba(244, 63, 94, 0.25);
  --accent-amber: #f59e0b;
  --accent-purple: #8b5cf6;
  --text-primary: #f8fafc;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --border-color: rgba(255, 255, 255, 0.08);
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --font-sans: 'Inter', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --transition-fast: 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-smooth: 0.35s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
  background-color: var(--bg-primary);
  color: var(--text-primary);
  font-family: var(--font-sans);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  overflow-x: hidden;
  background-image: 
    radial-gradient(circle at 15% 15%, rgba(6, 182, 212, 0.08) 0%, transparent 40%),
    radial-gradient(circle at 85% 85%, rgba(139, 92, 246, 0.08) 0%, transparent 40%);
  background-attachment: fixed;
}

/* Header & Navigation */
header {
  background: rgba(15, 23, 42, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 0;
  z-index: 100;
}

.header-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 1rem 1.5rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
}

.logo-badge {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.logo-icon {
  width: 42px;
  height: 42px;
  background: linear-gradient(135deg, var(--accent-cyan), var(--accent-purple));
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.4rem;
  box-shadow: 0 4px 15px var(--accent-cyan-glow);
}

.logo-text h1 {
  font-size: 1.25rem;
  font-weight: 800;
  letter-spacing: -0.5px;
  background: linear-gradient(to right, #ffffff, #cbd5e1);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

.logo-text p {
  font-size: 0.75rem;
  color: var(--accent-cyan);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 1px;
}

.nav-tabs {
  display: flex;
  background: var(--bg-secondary);
  padding: 0.35rem;
  border-radius: var(--radius-md);
  border: 1px solid var(--border-color);
  gap: 0.25rem;
}

.nav-btn {
  background: transparent;
  border: none;
  color: var(--text-secondary);
  padding: 0.55rem 1rem;
  font-size: 0.88rem;
  font-weight: 600;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: var(--transition-fast);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

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

.nav-btn.active {
  background: linear-gradient(135deg, var(--accent-cyan), #0284c7);
  color: #ffffff;
  box-shadow: 0 2px 10px var(--accent-cyan-glow);
}

/* Main Container */
main {
  max-width: 1100px;
  margin: 2rem auto;
  padding: 0 1.5rem;
  flex: 1;
  width: 100%;
}

.tab-pane {
  display: none;
  animation: fadeIn 0.3s ease-out;
}

.tab-pane.active {
  display: block;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

/* Glassmorphism Card Style */
.card-glass {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 2rem;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.25);
  position: relative;
  overflow: hidden;
}

/* SECTION 1: QUIZ ENGINE */
.quiz-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1.5rem;
  flex-wrap: wrap;
  gap: 1rem;
}

.quiz-badge {
  background: rgba(6, 182, 212, 0.15);
  color: var(--accent-cyan);
  padding: 0.35rem 0.85rem;
  border-radius: 999px;
  font-size: 0.8rem;
  font-weight: 700;
  text-transform: uppercase;
  border: 1px solid rgba(6, 182, 212, 0.3);
}

.quiz-stats {
  display: flex;
  align-items: center;
  gap: 1.25rem;
  font-size: 0.9rem;
  color: var(--text-secondary);
}

.stat-item {
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.stat-item strong {
  color: var(--text-primary);
}

.progress-bar-container {
  width: 100%;
  height: 8px;
  background: var(--bg-tertiary);
  border-radius: 999px;
  margin-bottom: 2rem;
  overflow: hidden;
}

.progress-bar {
  height: 100%;
  background: linear-gradient(90deg, var(--accent-cyan), var(--accent-emerald));
  width: 0%;
  transition: width 0.4s ease;
}

.question-text {
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 1.75rem;
  line-height: 1.5;
}

.options-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.option-btn {
  background: rgba(255, 255, 255, 0.03);
  border: 2px solid rgba(255, 255, 255, 0.08);
  border-radius: var(--radius-md);
  padding: 1.15rem 1.25rem;
  color: var(--text-primary);
  text-align: left;
  font-size: 1rem;
  font-family: inherit;
  cursor: pointer;
  transition: var(--transition-fast);
  display: flex;
  align-items: center;
  gap: 1rem;
  position: relative;
}

.option-letter {
  width: 32px;
  height: 32px;
  background: var(--bg-tertiary);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 0.88rem;
  color: var(--text-secondary);
  flex-shrink: 0;
  transition: var(--transition-fast);
}

.option-btn:hover:not(:disabled) {
  border-color: var(--accent-cyan);
  background: rgba(6, 182, 212, 0.05);
  transform: translateX(4px);
}

.option-btn:hover:not(:disabled) .option-letter {
  background: var(--accent-cyan);
  color: #ffffff;
}

.option-btn.correct {
  border-color: var(--accent-emerald) !important;
  background: rgba(16, 185, 129, 0.15) !important;
}

.option-btn.correct .option-letter {
  background: var(--accent-emerald);
  color: white;
}

.option-btn.wrong {
  border-color: var(--accent-rose) !important;
  background: rgba(244, 63, 94, 0.15) !important;
}

.option-btn.wrong .option-letter {
  background: var(--accent-rose);
  color: white;
}

.feedback-box {
  display: none;
  background: var(--bg-tertiary);
  border-radius: var(--radius-md);
  padding: 1.25rem;
  margin-bottom: 1.5rem;
  border-left: 5px solid var(--accent-cyan);
  animation: slideDown 0.3s ease;
}

@keyframes slideDown {
  from { opacity: 0; transform: translateY(-10px); }
  to { opacity: 1; transform: translateY(0); }
}

.feedback-box.correct-box {
  border-left-color: var(--accent-emerald);
  background: rgba(16, 185, 129, 0.1);
}

.feedback-box.wrong-box {
  border-left-color: var(--accent-rose);
  background: rgba(244, 63, 94, 0.1);
}

.feedback-title {
  font-weight: 700;
  margin-bottom: 0.35rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.feedback-text {
  color: #cbd5e1;
  font-size: 0.95rem;
  margin-bottom: 0.6rem;
}

.feedback-tip {
  font-size: 0.85rem;
  color: var(--accent-amber);
  background: rgba(245, 158, 11, 0.1);
  padding: 0.5rem 0.75rem;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.quiz-footer {
  display: flex;
  justify-content: flex-end;
}

.btn-primary {
  background: linear-gradient(135deg, var(--accent-cyan), #0284c7);
  color: white;
  border: none;
  padding: 0.85rem 1.75rem;
  font-size: 1rem;
  font-weight: 700;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: var(--transition-fast);
  display: flex;
  align-items: center;
  gap: 0.6rem;
  box-shadow: 0 4px 15px var(--accent-cyan-glow);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(6, 182, 212, 0.4);
}

/* Quiz End Screen */
.quiz-result-view {
  display: none;
  text-align: center;
  padding: 3rem 1rem;
}

.result-circle {
  width: 140px;
  height: 140px;
  border-radius: 50%;
  margin: 0 auto 1.5rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  background: radial-gradient(circle, var(--bg-tertiary), var(--bg-secondary));
  border: 4px solid var(--accent-cyan);
  box-shadow: 0 0 30px var(--accent-cyan-glow);
}

.result-score {
  font-size: 2.2rem;
  font-weight: 900;
  color: var(--text-primary);
}

.result-max {
  font-size: 0.85rem;
  color: var(--text-secondary);
}

.result-title {
  font-size: 1.75rem;
  margin-bottom: 0.5rem;
}

.result-desc {
  color: var(--text-secondary);
  max-width: 500px;
  margin: 0 auto 2rem;
}

.result-actions {
  display: flex;
  justify-content: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.btn-secondary {
  background: var(--bg-tertiary);
  color: var(--text-primary);
  border: 1px solid var(--border-color);
  padding: 0.85rem 1.5rem;
  font-size: 0.95rem;
  font-weight: 600;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: var(--transition-fast);
}

.btn-secondary:hover {
  background: rgba(255, 255, 255, 0.1);
}

/* SECTION 2: FLASHCARDS (ACTIVE RECALL) */
.flashcards-container {
  max-width: 650px;
  margin: 0 auto;
}

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

.filter-group {
  display: flex;
  gap: 0.5rem;
}

.filter-btn {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  padding: 0.4rem 0.8rem;
  font-size: 0.8rem;
  border-radius: 999px;
  cursor: pointer;
  transition: var(--transition-fast);
}

.filter-btn.active {
  background: var(--accent-cyan);
  color: #fff;
  border-color: var(--accent-cyan);
}

.flashcard-scene {
  perspective: 1000px;
  margin-bottom: 1.75rem;
  cursor: pointer;
}

.flashcard {
  width: 100%;
  min-height: 320px;
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
  border-radius: var(--radius-lg);
  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.35);
}

.flashcard.flipped {
  transform: rotateY(180deg);
}

.card-face {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  border-radius: var(--radius-lg);
  padding: 2.25rem;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  border: 1px solid var(--border-color);
}

.card-front {
  background: linear-gradient(145deg, #1e293b, #0f172a);
}

.card-back {
  background: linear-gradient(145deg, #1e293b, #111827);
  transform: rotateY(180deg);
  border-color: rgba(6, 182, 212, 0.3);
}

.card-header-tag {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  color: var(--accent-cyan);
  letter-spacing: 0.5px;
}

.card-flip-prompt {
  color: var(--text-muted);
  font-size: 0.8rem;
  display: flex;
  align-items: center;
  gap: 0.35rem;
}

.card-main-content {
  font-size: 1.3rem;
  font-weight: 600;
  text-align: center;
  color: var(--text-primary);
  margin: auto 0;
  white-space: pre-line;
  line-height: 1.6;
}

.card-back .card-main-content {
  font-size: 1.15rem;
  font-weight: 500;
  color: #e2e8f0;
}

.card-mnemonic {
  background: rgba(245, 158, 11, 0.1);
  border: 1px solid rgba(245, 158, 11, 0.25);
  padding: 0.6rem 0.9rem;
  border-radius: var(--radius-sm);
  color: var(--accent-amber);
  font-size: 0.85rem;
  text-align: center;
}

.flashcard-controls {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1rem;
}

.rating-btn {
  border: none;
  padding: 0.9rem;
  border-radius: var(--radius-md);
  font-weight: 700;
  font-size: 0.95rem;
  cursor: pointer;
  transition: var(--transition-fast);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.3rem;
}

.btn-again {
  background: rgba(244, 63, 94, 0.15);
  color: #fda4af;
  border: 1px solid rgba(244, 63, 94, 0.3);
}
.btn-again:hover {
  background: var(--accent-rose);
  color: #fff;
}

.btn-medium {
  background: rgba(245, 158, 11, 0.15);
  color: #fde68a;
  border: 1px solid rgba(245, 158, 11, 0.3);
}
.btn-medium:hover {
  background: var(--accent-amber);
  color: #fff;
}

.btn-good {
  background: rgba(16, 185, 129, 0.15);
  color: #a7f3d0;
  border: 1px solid rgba(16, 185, 129, 0.3);
}
.btn-good:hover {
  background: var(--accent-emerald);
  color: #fff;
}

/* SECTION 3: SIMULATEUR & CALCULATEUR */
.calc-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2rem;
  margin-top: 1.5rem;
}

@media (max-width: 768px) {
  .calc-grid {
    grid-template-columns: 1fr;
  }
}

.input-group {
  margin-bottom: 1.25rem;
}

.input-label {
  display: block;
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--text-secondary);
  margin-bottom: 0.5rem;
}

.input-with-unit {
  display: flex;
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-sm);
  overflow: hidden;
}

.input-with-unit input, .input-with-unit select {
  background: transparent;
  border: none;
  color: var(--text-primary);
  padding: 0.75rem 1rem;
  font-size: 1rem;
  font-family: inherit;
  outline: none;
}

.input-with-unit input {
  flex: 1;
}

.input-with-unit select {
  background: var(--bg-tertiary);
  color: var(--accent-cyan);
  font-weight: 600;
  cursor: pointer;
}

.results-display {
  background: var(--bg-primary);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-md);
  padding: 1.5rem;
}

.result-card-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.75rem 0;
  border-bottom: 1px solid rgba(255, 255, 255, 0.05);
}

.result-card-item:last-child {
  border-bottom: none;
}

.result-card-item .label {
  color: var(--text-secondary);
  font-size: 0.9rem;
}

.result-card-item .val {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--accent-cyan);
  font-family: monospace;
}

/* SECTION 4: CHEATSHEET / COURS */
.cheat-section {
  margin-bottom: 2rem;
}

.cheat-section h3 {
  color: var(--accent-cyan);
  font-size: 1.25rem;
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.cheat-table {
  width: 100%;
  border-collapse: collapse;
  margin: 1rem 0;
  background: var(--bg-primary);
  border-radius: var(--radius-sm);
  overflow: hidden;
}

.cheat-table th, .cheat-table td {
  padding: 0.85rem 1rem;
  text-align: left;
  border-bottom: 1px solid var(--border-color);
  font-size: 0.9rem;
}

.cheat-table th {
  background: rgba(255, 255, 255, 0.05);
  color: var(--text-secondary);
  font-weight: 700;
}

.formula-banner {
  background: linear-gradient(135deg, rgba(6, 182, 212, 0.1), rgba(139, 92, 246, 0.1));
  border: 1px solid rgba(6, 182, 212, 0.3);
  padding: 1.5rem;
  border-radius: var(--radius-md);
  text-align: center;
  margin: 1.5rem 0;
}

.formula-main {
  font-size: 2rem;
  font-weight: 800;
  color: #fff;
  letter-spacing: 1px;
}

/* Styles pour les fractions mathématiques et exemples */
.fraction {
  display: inline-flex;
  flex-direction: column;
  vertical-align: middle;
  text-align: center;
  padding: 0 0.25rem;
  font-size: 0.95em;
}

.fraction .num {
  border-bottom: 2px solid currentColor;
  padding-bottom: 2px;
  line-height: 1.1;
}

.fraction .denom {
  padding-top: 2px;
  line-height: 1.1;
}

.fraction-formula {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  margin: 0.6rem 0;
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--accent-cyan);
}

.card-example {
  background: rgba(255, 255, 255, 0.04);
  border: 1px dashed rgba(255, 255, 255, 0.18);
  border-radius: var(--radius-sm);
  padding: 0.75rem 1rem;
  margin-top: 0.6rem;
  font-size: 0.9rem;
  line-height: 1.5;
  text-align: left;
  color: #cbd5e1;
}

/* Responsive */
@media (max-width: 640px) {
  .header-container {
    flex-direction: column;
    align-items: stretch;
  }
  .nav-tabs {
    overflow-x: auto;
  }
  .card-glass {
    padding: 1.25rem;
  }
  .question-text {
    font-size: 1.15rem;
  }
}