.flashcards{max-width:1200px;margin:0 auto;padding:2rem}.flashcards-header{text-align:center;margin-bottom:2rem}.flashcards-header h1{font-size:2.5rem;color:#2d3748;margin-bottom:.5rem}.subtitle{color:#718096;font-size:1.1rem}.filters{display:flex;gap:1.5rem;margin-bottom:1.5rem;flex-wrap:wrap;background:#fff;padding:1.5rem;border-radius:12px;box-shadow:0 2px 8px #0000001a}.filter-group{display:flex;flex-direction:column;gap:.5rem;flex:1;min-width:200px}.filter-group label{font-weight:600;color:#4a5568;font-size:.9rem}.filter-select{padding:.75rem;border:2px solid #e2e8f0;border-radius:8px;font-size:1rem;background:#fff;cursor:pointer;transition:all .2s}.filter-select:hover{border-color:#667eea}.filter-select:focus{outline:none;border-color:#667eea;box-shadow:0 0 0 3px #667eea1a}.display-options{display:flex;gap:2rem;margin-bottom:1.5rem;padding:1rem;background:#f7fafc;border-radius:8px}.checkbox-label{display:flex;align-items:center;gap:.5rem;font-weight:500;color:#4a5568;cursor:pointer}.checkbox-label input[type=checkbox]{width:18px;height:18px;cursor:pointer}.progress-stats{display:flex;gap:2rem;justify-content:center;margin-bottom:1rem}.stat{display:flex;flex-direction:column;align-items:center;gap:.25rem}.stat-label{font-size:.85rem;color:#718096;font-weight:500}.stat-value{font-size:1.5rem;font-weight:700;color:#2d3748}.progress-bar{height:8px;background:#e2e8f0;border-radius:999px;overflow:hidden;margin-bottom:2rem}.progress-fill{height:100%;background:linear-gradient(90deg,#667eea,#764ba2);transition:width .3s ease}.flashcard-container{perspective:1000px;margin-bottom:2rem;min-height:400px;display:flex;align-items:center;justify-content:center}.flashcard{width:100%;max-width:600px;height:400px;position:relative;transform-style:preserve-3d;transition:transform .6s;cursor:pointer}.flashcard.flipped{transform:rotateY(180deg)}.flashcard-front,.flashcard-back{position:absolute;width:100%;height:100%;backface-visibility:hidden;border-radius:16px;display:flex;flex-direction:column;align-items:center;justify-content:center;padding:2rem;box-shadow:0 10px 30px #00000026}.flashcard-front{background:linear-gradient(135deg,#667eea,#764ba2);color:#fff}.flashcard-back{background:#fff;transform:rotateY(180deg);overflow-y:auto}.card-category{position:absolute;top:1rem;left:1rem;background:#fff3;padding:.5rem 1rem;border-radius:20px;font-size:.85rem;font-weight:600}.card-difficulty{position:absolute;top:1rem;right:1rem;font-size:1.2rem}.card-word{font-size:3rem;font-weight:700;text-align:center;margin:1rem 0}.card-hint{position:absolute;bottom:1.5rem;font-size:.9rem;opacity:.8;font-style:italic}.translation{width:100%;margin-bottom:1.5rem;text-align:center}.language-tag{display:inline-block;font-size:.85rem;font-weight:600;color:#718096;margin-bottom:.5rem}.translation-text{font-size:2rem;font-weight:700;color:#2d3748;margin-top:.5rem}.chinese .translation-text{color:#e53e3e}.english .translation-text{color:#3182ce}.example{width:100%;margin-top:1.5rem;padding-top:1.5rem;border-top:2px solid #e2e8f0}.example-label{font-weight:600;color:#4a5568;margin-bottom:.75rem;font-size:.9rem}.example-text{font-size:1.1rem;color:#2d3748;font-style:italic;margin-bottom:.5rem;line-height:1.6}.example-translation{font-size:.95rem;color:#718096;line-height:1.6}.controls{display:flex;justify-content:space-between;align-items:center;gap:1rem;margin-bottom:2rem;max-width:600px;margin-left:auto;margin-right:auto}.mastery-controls{flex:1;display:flex;justify-content:center}.btn{padding:.75rem 1.5rem;border:none;border-radius:8px;font-size:1rem;font-weight:600;cursor:pointer;transition:all .2s;white-space:nowrap}.btn:disabled{opacity:.5;cursor:not-allowed}.btn-primary{background:linear-gradient(135deg,#667eea,#764ba2);color:#fff}.btn-primary:hover:not(:disabled){transform:translateY(-2px);box-shadow:0 4px 12px #667eea66}.btn-secondary{background:#e2e8f0;color:#2d3748}.btn-secondary:hover:not(:disabled){background:#cbd5e0}.btn-success{background:#48bb78;color:#fff}.btn-success:hover{background:#38a169;transform:translateY(-2px)}.btn-warning{background:#ed8936;color:#fff}.btn-warning:hover{background:#dd6b20;transform:translateY(-2px)}.btn-outline{background:transparent;border:2px solid #667eea;color:#667eea}.btn-outline:hover{background:#667eea;color:#fff}.keyboard-hints{display:flex;justify-content:center;gap:1.5rem;margin-bottom:2rem;font-size:.9rem;color:#718096}.keyboard-hints span:first-child{font-weight:600}.stats-summary{background:#fff;padding:2rem;border-radius:12px;box-shadow:0 2px 8px #0000001a;margin-bottom:2rem}.stats-summary h3{text-align:center;color:#2d3748;margin-bottom:1.5rem;font-size:1.5rem}.stats-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(150px,1fr));gap:1.5rem}.stat-box{text-align:center;padding:1.5rem;background:linear-gradient(135deg,#f7fafc,#edf2f7);border-radius:12px;transition:transform .2s}.stat-box:hover{transform:translateY(-4px)}.stat-box .stat-number{font-size:2.5rem;font-weight:700;color:#667eea;margin-bottom:.5rem}.stat-box .stat-label{font-size:.9rem;color:#4a5568;font-weight:500}.reset-section{text-align:center;margin-top:2rem}.empty-state{text-align:center;padding:4rem 2rem;background:#fff;border-radius:16px;box-shadow:0 4px 16px #0000001a}.empty-icon{font-size:5rem;margin-bottom:1rem}.empty-state h2{color:#2d3748;margin-bottom:1rem}.empty-state p{color:#718096;margin-bottom:2rem;font-size:1.1rem}@media(max-width:768px){.flashcards{padding:1rem}.flashcards-header h1{font-size:1.8rem}.filters{flex-direction:column}.filter-group{min-width:100%}.flashcard-container{min-height:350px}.flashcard{height:350px}.card-word{font-size:2rem}.translation-text{font-size:1.5rem}.controls{flex-direction:column}.mastery-controls,.btn{width:100%}.stats-grid{grid-template-columns:repeat(2,1fr)}.keyboard-hints{flex-direction:column;gap:.5rem}}