:root{--primary: #4f46e5;--primary-hover: #4338ca;--bg-color: #f3f4f6;--card-bg: #ffffff;--text-main: #1f2937;--text-muted: #6b7280;--danger: #ef4444;--success: #10b981;--radius: 12px;--shadow: 0 4px 6px -1px rgba(0, 0, 0, .1), 0 2px 4px -1px rgba(0, 0, 0, .06)}*{box-sizing:border-box;margin:0;padding:0}body{font-family:Segoe UI,Tahoma,Geneva,Verdana,sans-serif;background-color:var(--bg-color);color:var(--text-main);line-height:1.5;min-height:100vh;display:flex;justify-content:center}#root{width:100%;max-width:800px;margin:0 auto;padding:20px}.app-header{display:flex;justify-content:space-between;align-items:center;background:var(--card-bg);padding:15px 20px;border-radius:var(--radius);box-shadow:var(--shadow);margin-bottom:30px}.app-title{font-size:1.25rem;font-weight:700;color:var(--primary);justify-content:center;justify-self:center}.user-info{display:flex;align-items:center;gap:15px;font-size:.9rem}.card{background:var(--card-bg);padding:30px;border-radius:var(--radius);box-shadow:var(--shadow);text-align:center;max-width:450px;margin:0 auto}.form-group{margin-bottom:20px}.input-field{width:100%;padding:12px 15px;border:2px solid #e5e7eb;border-radius:8px;font-size:1rem;transition:border-color .3s;outline:none}.input-field:focus{border-color:var(--primary)}.btn{display:inline-block;padding:12px 24px;background-color:var(--primary);color:#fff;border:none;border-radius:8px;font-size:1rem;font-weight:600;cursor:pointer;transition:background .3s,transform .1s;width:100%}.btn:hover{background-color:var(--primary-hover)}.btn:active{transform:scale(.98)}.btn-danger{background-color:transparent;color:var(--danger);border:1px solid var(--danger);padding:6px 12px;font-size:.85rem;width:auto}.btn-danger:hover{background-color:var(--danger);color:#fff}@media(max-width:600px){#root{padding:10px}.app-header{flex-direction:column;gap:10px;text-align:center}.card{padding:20px}}.category-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(250px,1fr));gap:20px;width:100%;margin-top:20px}.category-card{background:#fff;padding:25px;border-radius:var(--radius);box-shadow:var(--shadow);cursor:pointer;transition:transform .2s,box-shadow .2s,border-color .2s;border:2px solid transparent;display:flex;flex-direction:column;justify-content:space-between;min-height:150px}.category-card:hover{transform:translateY(-5px);box-shadow:0 10px 15px -3px #0000001a;border-color:var(--primary)}.category-card h3{color:var(--text-main);margin-bottom:10px}.category-card p{color:var(--text-muted);font-size:.9rem;margin-bottom:15px}.start-badge{align-self:flex-start;font-size:.85rem;color:var(--primary);font-weight:700}.quiz-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:20px;font-weight:700;color:var(--text-muted)}.question-text{margin-bottom:20px;color:var(--text-main)}.answers-area{text-align:left;margin-bottom:30px}.quiz-footer{display:flex;justify-content:space-between;margin-top:20px}.btn-small{background:transparent;border:1px solid #ccc;padding:5px 10px;border-radius:6px;cursor:pointer}.nav-grid{display:flex;flex-wrap:wrap;gap:8px;margin-bottom:20px;justify-content:center}.nav-item{width:35px;height:35px;border-radius:50%;border:1px solid #ccc;display:flex;align-items:center;justify-content:center;font-size:.9rem;font-weight:700;cursor:pointer;background:#fff;transition:all .2s}.nav-item.active{border-color:var(--primary);border-width:2px;transform:scale(1.1)}.status-default{background:#fff;color:var(--text-main)}.status-visited{background:#e5e7eb;color:var(--text-main)}.status-correct{background:var(--success);color:#fff;border-color:var(--success)}.status-wrong{background:var(--danger);color:#fff;border-color:var(--danger)}.status-pending{background:#3b82f6;color:#fff;border-color:#3b82f6}.option-item{display:flex;align-items:center;padding:12px;margin:8px 0;border:1px solid #e5e7eb;border-radius:8px;cursor:pointer;transition:background .2s}.option-item:hover{background:#f9fafb}.option-item.disabled{pointer-events:none;opacity:.8}.option-item.selected-correct{background:#d1fae5;border-color:var(--success)}.option-item.selected-wrong{background:#fee2e2;border-color:var(--danger)}.feedback-box{margin-top:15px;padding:15px;border-radius:8px;font-weight:500}.feedback-correct{background:#d1fae5;color:#065f46}.feedback-wrong{background:#fee2e2;color:#991b1b}.flashcard-container{perspective:1000px;width:100%;height:350px;margin:20px auto;cursor:pointer;position:relative}.flashcard-inner{position:relative;width:100%;height:100%;text-align:center;transition:transform .6s;transform-style:preserve-3d;border-radius:var(--radius);box-shadow:var(--shadow)}.flashcard-container.flipped .flashcard-inner{transform:rotateY(180deg)}.flashcard-front,.flashcard-back{position:absolute;width:100%;height:100%;-webkit-backface-visibility:hidden;backface-visibility:hidden;display:flex;flex-direction:column;align-items:center;justify-content:center;padding:30px;border-radius:var(--radius);background:#fff;border:2px solid transparent}.flashcard-front{color:var(--text-main);font-size:1.2rem;font-weight:500;z-index:2}.flashcard-back{background-color:var(--primary);color:#fff;transform:rotateY(180deg);font-size:1.3rem;font-weight:700}.flashcard-hint{margin-top:20px;font-size:.85rem;color:var(--text-muted);font-weight:400}@media(max-width:600px){.nav-grid{gap:12px}.nav-item{width:44px;height:44px;font-size:1.1rem}.quiz-question-title{font-size:1.25rem;line-height:1.5}.option-item{padding:16px;margin-bottom:12px;font-size:1.05rem}.quiz-header{flex-direction:column;gap:15px;text-align:center}.quiz-header>div{width:100%;justify-content:center;display:flex;gap:10px}.quiz-footer-nav .btn{flex:1;padding:14px;font-size:1.1rem}.btn{padding:14px}}.btn-danger{background-color:#ef4444;color:#fff}.category-card-static{cursor:default;transform:none}.category-actions{display:flex;gap:15px;margin-top:15px}.category-actions .btn{flex:1;width:auto}.btn-quiz{font-size:.9rem;padding:10px}.btn-flashcards{font-size:.9rem;padding:10px;background:#8b5cf6;color:#fff}.quiz-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:20px;background:#fff;padding:10px;border-radius:12px;box-shadow:0 2px 5px #0000000d}.quiz-main-card{text-align:left;max-width:100%;margin-bottom:20px}.quiz-question-title{margin-bottom:20px}.quiz-footer-nav{margin-bottom:30px;display:flex;justify-content:space-between}.nav-divider{border:0;border-top:1px solid #ddd;margin:20px 0}.feedback-box-success{padding:10px;background-color:#dcfce7;color:#166534;border-radius:6px;margin-top:10px}.feedback-box-error{padding:10px;background-color:#fee2e2;color:#991b1b;border-radius:6px;margin-top:10px}.feedback-box-info{padding:10px;background:#eff6ff;color:#1e40af;border-radius:6px;margin-top:10px}.input-field{width:100%;padding:10px;border:1px solid #ccc;border-radius:6px;margin-top:10px}.result-card{text-align:center;padding:40px}.result-icon{font-size:3rem;margin-bottom:20px}.result-text{font-size:1.2rem;margin:20px 0}.app-container{max-width:800px;margin:0 auto}.error-card{text-align:center;padding:40px;background-color:#fee2e2;color:#991b1b;border-radius:12px}