.btn{padding:var(--spacing-md) var(--spacing-lg);border-radius:var(--border-radius);font-size:16px;font-weight:500;cursor:pointer;transition:all .2s ease;min-width:120px}.btn-primary{background-color:var(--primary-color);color:#fff}.btn-primary:hover:not(:disabled){background-color:#0056b3;transform:translateY(-1px)}.btn-secondary{background-color:#f0f0f0;color:var(--text-color)}.btn-secondary:hover:not(:disabled){background-color:#e0e0e0}.btn:disabled{opacity:.5;cursor:not-allowed}.login-page{min-height:100vh;display:flex;align-items:center;justify-content:center;background-color:var(--background-color);padding:var(--spacing-lg)}.login-container{width:100%;max-width:400px;background:#fff;padding:var(--spacing-xl);border-radius:var(--border-radius);box-shadow:0 4px 12px #0000001a}.login-container h1{text-align:center;margin-bottom:var(--spacing-xl);font-size:28px;font-weight:600}.login-form{display:flex;flex-direction:column;gap:var(--spacing-md)}.form-group{display:flex;flex-direction:column;gap:var(--spacing-xs)}.form-group label{font-size:14px;font-weight:500;color:var(--text-color)}.form-group input{padding:var(--spacing-md);border:1px solid var(--border-color);border-radius:var(--border-radius);font-size:16px;transition:border-color .2s}.form-group input:focus{border-color:var(--primary-color)}.error-message{color:#ff3b30;font-size:14px;text-align:center;padding:var(--spacing-sm)}.full-width{width:100%;margin-top:var(--spacing-md)}.register-link{text-align:center;margin-top:var(--spacing-md);font-size:14px;color:var(--text-secondary)}.register-link a{color:var(--primary-color);font-weight:500}.home-page{min-height:100vh;padding:var(--spacing-lg);max-width:600px;margin:0 auto}.home-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:var(--spacing-xl)}.home-header h1{font-size:24px;font-weight:600}.logout-btn{padding:var(--spacing-sm) var(--spacing-md);background:#f0f0f0;border-radius:var(--border-radius);font-size:14px;color:var(--text-color);cursor:pointer}.logout-btn:hover{background:#e0e0e0}.home-content{display:flex;flex-direction:column;align-items:center;gap:var(--spacing-xl);margin-top:var(--spacing-xl)}.welcome-section{text-align:center}.welcome-section h2{font-size:28px;margin-bottom:var(--spacing-md)}.welcome-section p{color:var(--text-secondary);font-size:16px}.start-button{padding:var(--spacing-lg) var(--spacing-xl);font-size:18px;min-width:200px}.language-select-page{min-height:100vh;display:flex;align-items:center;justify-content:center;padding:var(--spacing-lg)}.language-select-container{width:100%;max-width:500px;background:#fff;padding:var(--spacing-xl);border-radius:var(--border-radius);box-shadow:0 4px 12px #0000001a}.language-select-container h1{text-align:center;margin-bottom:var(--spacing-xl);font-size:24px;font-weight:600}.select-group{margin-bottom:var(--spacing-lg)}.select-group label{display:block;margin-bottom:var(--spacing-sm);font-size:14px;font-weight:500;color:var(--text-color)}.mode-circle-group{display:flex;gap:var(--spacing-md);flex-wrap:wrap}.mode-circle{width:96px;height:96px;border-radius:50%;border:2px solid var(--border-color);background:#fff;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:var(--spacing-xs);cursor:pointer;transition:all .2s ease;font-size:16px}.mode-circle-sub{font-size:12px;color:var(--text-secondary);letter-spacing:.5px}.mode-circle:hover{border-color:var(--primary-color);box-shadow:0 4px 12px #3563e926}.mode-circle.active{background:linear-gradient(135deg,#3d6be0,#5f8bff);color:#fff;border-color:transparent}.mode-circle.active .mode-circle-sub{color:#fffc}@media(max-width:600px){.mode-circle{width:80px;height:80px;font-size:14px}}.select-input{width:100%;padding:var(--spacing-md);border:1px solid var(--border-color);border-radius:var(--border-radius);font-size:16px;background:#fff;cursor:pointer}.select-input:focus{outline:none;border-color:var(--primary-color)}.action-buttons{display:flex;gap:var(--spacing-md);margin-top:var(--spacing-lg)}.start-button{flex:1}.refresh-button{flex:1;background:var(--border-color);color:var(--text-color)}.slider-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:var(--spacing-sm)}.slider-header label{margin-bottom:0}.slider-value{font-size:14px;color:var(--text-secondary)}.slider-input{width:100%;-webkit-appearance:none;height:6px;border-radius:999px;background:linear-gradient(90deg,#e3e8ff,#cad4ff);outline:none;margin:var(--spacing-sm) 0}.slider-input::-webkit-slider-thumb{-webkit-appearance:none;width:20px;height:20px;border-radius:50%;background:#3d6be0;box-shadow:0 4px 10px #3d6be066;cursor:pointer;transition:transform .2s ease}.slider-input::-webkit-slider-thumb:active{transform:scale(1.1)}.slider-input::-moz-range-thumb{width:20px;height:20px;border-radius:50%;background:#3d6be0;border:none;box-shadow:0 4px 10px #3d6be066;cursor:pointer}.slider-scale{display:flex;justify-content:space-between;font-size:12px;color:var(--text-secondary)}.word-card-container{width:100%;max-width:500px;margin:0 auto;position:relative}.word-card{position:relative;width:100%;min-height:300px}.word-card-front,.word-card-back{position:absolute;width:100%;min-height:300px;border-radius:var(--border-radius);padding:var(--spacing-xl);display:flex;flex-direction:column;justify-content:center;align-items:center;background:#fff;box-shadow:0 4px 12px #0000001a;-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale;transition:opacity .5s cubic-bezier(.4,0,.2,1),visibility .5s cubic-bezier(.4,0,.2,1);opacity:1;visibility:visible;will-change:opacity;transform:translateZ(0)}.word-card-back,.word-card.flipped .word-card-front{opacity:0;visibility:hidden;pointer-events:none}.word-card.flipped .word-card-back{opacity:1;visibility:visible;pointer-events:auto}.word-text{font-size:32px;font-weight:600;color:var(--text-color);margin-bottom:var(--spacing-md);text-align:center}.part-of-speech{font-size:14px;color:var(--text-secondary);margin-bottom:var(--spacing-lg)}.pronunciation{font-size:18px;color:var(--text-secondary);margin-bottom:var(--spacing-sm)}.pronunciation-secondary{font-size:16px;margin-top:-var(--spacing-sm);margin-bottom:var(--spacing-md)}.example{margin-top:var(--spacing-lg);width:100%;text-align:center}.example-foreign{font-size:16px;color:var(--text-color);margin-bottom:var(--spacing-sm);font-style:italic;line-height:1.6}.example-chinese{font-size:15px;color:var(--text-secondary);line-height:1.6}.hint{position:absolute;bottom:var(--spacing-md);font-size:12px;color:var(--text-secondary)}.hint-text{margin-top:var(--spacing-lg);font-size:14px;color:var(--text-secondary);font-style:italic;text-align:center}.answer-buttons{display:flex;gap:var(--spacing-md);margin-top:var(--spacing-lg);justify-content:center}.btn-answer{padding:var(--spacing-sm) var(--spacing-lg);border-radius:var(--border-radius);font-size:14px;font-weight:500;cursor:pointer;border:none;transition:all .2s ease;min-width:80px}.btn-wrong{background-color:#ff3b30;color:#fff}.btn-wrong:hover{background-color:#d32f2f}.btn-learning{background-color:#ff9500;color:#fff}.btn-learning:hover{background-color:#e68900}.btn-correct{background-color:#34c759;color:#fff}.btn-correct:hover{background-color:#2ea043}.timer-display{position:absolute;top:var(--spacing-md);right:var(--spacing-md);z-index:10}.timer-circle{width:50px;height:50px;border-radius:50%;background-color:#34c759;color:#fff;display:flex;align-items:center;justify-content:center;font-size:20px;font-weight:600;box-shadow:0 2px 8px #0003;transition:all .3s ease}.timer-warning{background-color:#ff3b30;animation:pulse 1s infinite}@keyframes pulse{0%,to{transform:scale(1)}50%{transform:scale(1.1)}}.audio-play-button{margin-top:var(--spacing-md);margin-bottom:var(--spacing-sm);width:48px;height:48px;border-radius:50%;border:2px solid var(--primary-color, #007AFF);background:#fff;color:var(--primary-color, #007AFF);cursor:pointer;display:flex;align-items:center;justify-content:center;transition:all .2s ease;box-shadow:0 2px 8px #0000001a;padding:0}.audio-play-button:hover{background:var(--primary-color, #007AFF);color:#fff;transform:scale(1.1);box-shadow:0 4px 12px #007aff4d}.audio-play-button:active{transform:scale(.95)}.audio-play-button svg{width:24px;height:24px}.study-info{display:flex;flex-direction:column;gap:var(--spacing-xs);margin-top:var(--spacing-sm);margin-bottom:var(--spacing-sm);padding:var(--spacing-sm) var(--spacing-md);background:#007aff0d;border-radius:var(--border-radius);font-size:13px;color:var(--text-secondary);text-align:center}.study-info-item{display:inline-block;margin:0 var(--spacing-xs);padding:2px 8px;background:#007aff1a;border-radius:12px;font-weight:500;color:var(--primary-color, #007AFF)}.progress-bar-container{width:100%;max-width:500px;margin:0 auto}.progress-bar{width:100%;height:8px;background-color:#f0f0f0;border-radius:4px;overflow:hidden;margin-bottom:var(--spacing-xs)}.progress-bar-fill{height:100%;background-color:var(--primary-color);transition:width .3s ease}.progress-text{text-align:center;font-size:14px;color:var(--text-secondary)}.study-page{min-height:100vh;padding:var(--spacing-lg);max-width:600px;margin:0 auto;display:flex;flex-direction:column}.study-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:var(--spacing-lg)}.back-btn{padding:var(--spacing-sm) var(--spacing-md);background:#f0f0f0;border-radius:var(--border-radius);font-size:14px;cursor:pointer}.language-mode{font-size:14px;color:var(--text-secondary);text-transform:uppercase}.word-card-wrapper{flex:1;display:flex;align-items:center;justify-content:center;margin-top:var(--spacing-xl)}.loading,.error{text-align:center;padding:var(--spacing-xl);font-size:18px}.error{color:#ff3b30;margin-bottom:var(--spacing-lg)}.finish-container{text-align:center;padding:var(--spacing-xl)}.finish-container h2{font-size:28px;margin-bottom:var(--spacing-xl)}.score-display{text-align:center;margin-bottom:var(--spacing-xl);padding:var(--spacing-lg);background:#f8f9fa;border-radius:var(--border-radius)}.score-fraction{font-size:48px;font-weight:700;line-height:1.2;margin-bottom:var(--spacing-sm)}.score-numerator{color:#34c759}.score-divider{color:var(--text-secondary);margin:0 var(--spacing-xs)}.score-denominator{color:var(--text-primary)}.score-label{font-size:14px;color:var(--text-secondary)}.stats{display:flex;justify-content:center;gap:var(--spacing-xl);margin-bottom:var(--spacing-xl)}.stat-item{display:flex;flex-direction:column;align-items:center}.stat-value{font-size:32px;font-weight:600;margin-bottom:var(--spacing-xs)}.stat-value.correct{color:#34c759}.stat-value.wrong{color:#ff3b30}.stat-value.vague{color:#ff9500}.stat-label{font-size:14px;color:var(--text-secondary)}.finish-actions{display:flex;gap:var(--spacing-md);justify-content:center}.finish-actions button{flex:1}.app{min-height:100vh;display:flex;flex-direction:column}:root{--primary-color: #007AFF;--background-color: #FFFFFF;--text-color: #333333;--text-secondary: #666666;--border-color: #E5E5E5;--border-radius: 12px;--spacing-xs: 8px;--spacing-sm: 12px;--spacing-md: 16px;--spacing-lg: 24px;--spacing-xl: 32px}*{margin:0;padding:0;box-sizing:border-box}body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Oxygen,Ubuntu,Cantarell,Fira Sans,Droid Sans,Helvetica Neue,sans-serif;-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale;background-color:var(--background-color);color:var(--text-color);line-height:1.6}#root{min-height:100vh}button{font-family:inherit;cursor:pointer;border:none;outline:none;transition:all .2s ease}button:disabled{opacity:.5;cursor:not-allowed}input{font-family:inherit;outline:none}a{text-decoration:none;color:inherit}