:root{--color-primary: #3b82f6;--color-primary-dark: #2563eb;--color-secondary: #10b981;--color-warning: #f59e0b;--color-error: #ef4444;--color-background: #f8fafc;--color-card: #ffffff;--color-text: #1e293b;--color-text-secondary: #64748b;--color-border: #e2e8f0;--spacing-xs: .25rem;--spacing-sm: .5rem;--spacing-md: 1rem;--spacing-lg: 1.5rem;--spacing-xl: 2rem;--radius-sm: .375rem;--radius-md: .5rem;--radius-lg: 1rem;--shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, .05);--shadow-md: 0 4px 6px -1px rgba(0, 0, 0, .1);--shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, .1);--transition-fast: .15s ease;--transition-normal: .3s ease}*{box-sizing:border-box;margin:0;padding:0}body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,sans-serif;background:var(--color-background);color:var(--color-text);line-height:1.6;min-height:100vh}#app{max-width:800px;margin:0 auto;padding:var(--spacing-md)}.app-header{text-align:center;padding:var(--spacing-xl) 0}.app-title{font-size:2.5rem;font-weight:700;color:var(--color-primary);margin-bottom:var(--spacing-sm)}.app-title .icon{display:inline-block;animation:spin 3s linear infinite}@keyframes spin{0%{transform:rotate(0)}to{transform:rotate(360deg)}}.app-subtitle{color:var(--color-text-secondary);font-size:1.1rem}.mode-nav{display:flex;gap:var(--spacing-sm);margin-bottom:var(--spacing-xl);background:var(--color-card);padding:var(--spacing-sm);border-radius:var(--radius-lg);box-shadow:var(--shadow-sm)}.nav-button{flex:1;padding:var(--spacing-md);border:2px solid transparent;background:transparent;border-radius:var(--radius-md);font-size:1rem;font-weight:600;color:var(--color-text-secondary);cursor:pointer;transition:all var(--transition-fast);display:flex;align-items:center;justify-content:center;gap:var(--spacing-sm)}.nav-button:hover{background:var(--color-background)}.nav-button.active{background:var(--color-primary);color:#fff;border-color:var(--color-primary-dark)}.view{display:none}.view.active{display:block;animation:fadeIn var(--transition-normal)}@keyframes fadeIn{0%{opacity:0;transform:translateY(10px)}to{opacity:1;transform:translateY(0)}}.quiz-container,.flashcard-container,.timed-container,.progress-container{background:var(--color-card);border-radius:var(--radius-lg);padding:var(--spacing-xl);box-shadow:var(--shadow-md)}.question-header,.flashcard-header,.timed-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:var(--spacing-lg);padding-bottom:var(--spacing-md);border-bottom:2px solid var(--color-border)}.question-counter{font-weight:600;color:var(--color-text-secondary)}.grade-badge{display:inline-block;padding:.15rem .5rem;border-radius:var(--radius-sm);font-size:.75rem;font-weight:700;vertical-align:middle;margin-left:var(--spacing-sm)}.grade-4-5{background:#10b98126;color:#059669}.grade-6-8{background:#3b82f626;color:var(--color-primary-dark)}.grade-9-12{background:#8b5cf626;color:#7c3aed}.score{font-weight:700;font-size:1.2rem;color:var(--color-primary)}.question-card{margin-bottom:var(--spacing-xl)}.question-text{font-size:1.25rem;font-weight:600;margin-bottom:var(--spacing-lg);line-height:1.5}.options-container{display:flex;flex-direction:column;gap:var(--spacing-md)}.option-button{width:100%;padding:var(--spacing-lg);border:2px solid var(--color-border);background:#fff;border-radius:var(--radius-md);font-size:1rem;text-align:left;cursor:pointer;transition:all var(--transition-fast);min-height:44px}.option-button:hover:not(:disabled){border-color:var(--color-primary);background:#3b82f60d;transform:translateY(-2px);box-shadow:var(--shadow-sm)}.option-button:disabled{cursor:not-allowed;opacity:.6}.option-button.selected{border-color:var(--color-primary);background:#3b82f61a}.option-button.correct{border-color:var(--color-secondary);background:#10b9811a;animation:pulse .5s ease}.option-button.incorrect{border-color:var(--color-error);background:#ef44441a;animation:shake .5s ease}@keyframes pulse{0%,to{transform:scale(1)}50%{transform:scale(1.02)}}@keyframes shake{0%,to{transform:translate(0)}25%{transform:translate(-5px)}75%{transform:translate(5px)}}.feedback-container{margin-bottom:var(--spacing-lg);padding:var(--spacing-md);border-radius:var(--radius-md);animation:slideDown var(--transition-normal)}.feedback-container.hidden{display:none}.feedback-container.correct{background:#10b9811a;border:2px solid var(--color-secondary)}.feedback-container.incorrect{background:#ef44441a;border:2px solid var(--color-error)}@keyframes slideDown{0%{opacity:0;transform:translateY(-10px)}to{opacity:1;transform:translateY(0)}}.feedback-message{font-weight:600;font-size:1.1rem}.btn{padding:var(--spacing-md) var(--spacing-xl);border:none;border-radius:var(--radius-md);font-size:1rem;font-weight:600;cursor:pointer;transition:all var(--transition-fast);min-height:44px}.btn:disabled{opacity:.5;cursor:not-allowed}.btn-primary{background:var(--color-primary);color:#fff}.btn-primary:hover:not(:disabled){background:var(--color-primary-dark);transform:translateY(-2px);box-shadow:var(--shadow-md)}.btn-secondary{background:var(--color-border);color:var(--color-text)}.btn-secondary:hover:not(:disabled){background:var(--color-text-secondary);color:#fff}.btn-success{background:var(--color-secondary);color:#fff}.btn-warning{background:var(--color-warning);color:#fff}.btn-danger{background:var(--color-error);color:#fff}.quiz-actions,.flashcard-actions,.timed-actions,.progress-actions{display:flex;gap:var(--spacing-md);justify-content:center}.flashcard{perspective:1000px;height:400px;margin-bottom:var(--spacing-xl);cursor:pointer}.flashcard-inner{position:relative;width:100%;height:100%;transition:transform .6s;transform-style:preserve-3d}.flashcard.flipped .flashcard-inner{transform:rotateY(180deg)}.flashcard-front,.flashcard-back{position:absolute;width:100%;height:100%;backface-visibility:hidden;display:flex;align-items:center;justify-content:center;padding:var(--spacing-xl);background:linear-gradient(135deg,var(--color-primary) 0%,var(--color-primary-dark) 100%);color:#fff;border-radius:var(--radius-lg);box-shadow:var(--shadow-lg)}.flashcard-back{background:linear-gradient(135deg,var(--color-secondary) 0%,#059669 100%);transform:rotateY(180deg)}.flashcard-text{font-size:1.5rem;font-weight:600;text-align:center}.timer-display{display:flex;align-items:center;gap:var(--spacing-sm);font-size:1.5rem;font-weight:700;color:var(--color-primary)}.timer-display.warning{color:var(--color-warning);animation:blink 1s ease-in-out infinite}.timer-display.danger{color:var(--color-error);animation:timerPulse .5s ease-in-out infinite}@keyframes blink{0%,to{opacity:1}50%{opacity:.5}}@keyframes timerPulse{0%,to{transform:scale(1)}50%{transform:scale(1.15)}}.stats-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(150px,1fr));gap:var(--spacing-md);margin:var(--spacing-xl) 0}.stat-card{background:var(--color-background);padding:var(--spacing-lg);border-radius:var(--radius-md);text-align:center;border:2px solid var(--color-border)}.stat-card.mastered{border-color:var(--color-secondary);background:#10b9810d}.stat-card.learning{border-color:var(--color-warning);background:#f59e0b0d}.stat-card.new{border-color:var(--color-primary);background:#3b82f60d}.stat-card h3{font-size:2.5rem;font-weight:700;margin-bottom:var(--spacing-xs)}.stat-card p{color:var(--color-text-secondary);font-weight:600}.chart-container{margin:var(--spacing-xl) 0;background:var(--color-background);padding:var(--spacing-lg);border-radius:var(--radius-md)}.toast-container{position:fixed;bottom:var(--spacing-lg);right:var(--spacing-lg);z-index:1000;display:flex;flex-direction:column;gap:var(--spacing-sm)}.toast{background:var(--color-card);padding:var(--spacing-md) var(--spacing-lg);border-radius:var(--radius-md);box-shadow:var(--shadow-lg);animation:toastIn var(--transition-normal) ease;min-width:250px}@keyframes toastIn{0%{opacity:0;transform:translate(100%)}to{opacity:1;transform:translate(0)}}.toast.success{border-left:4px solid var(--color-secondary)}.toast.error{border-left:4px solid var(--color-error)}@media(max-width:600px){.app-title{font-size:2rem}.mode-nav{flex-wrap:wrap}.nav-button{flex:1 1 calc(50% - var(--spacing-sm))}.question-text{font-size:1.1rem}.flashcard{height:300px}.flashcard-text{font-size:1.2rem}}