@import "https://fonts.googleapis.com/css2?family=Fredoka:wght@400;500;600;700&family=Quicksand:wght@600;700&family=Noto+Sans+SC:wght@600;700&display=swap";:root{--font-main:"Fredoka", "Quicksand", -apple-system, sans-serif;--font-chinese:"Noto Sans SC", sans-serif;--bg-gradient:linear-gradient(135deg, #f0f9ff 0%, #fef2f2 50%, #f0fdf4 100%);--bi-red:#ef4444;--bi-red-dark:#b91c1c;--mandarin-blue:#0284c7;--mandarin-blue-dark:#0369a1;--gold-star:#f59e0b;--success-green:#22c55e;--success-green-dark:#15803d;--text-primary:#0f172a;--text-muted:#64748b;--radius-xl:24px;--radius-lg:18px;--radius-md:12px}*{box-sizing:border-box;-webkit-tap-highlight-color:transparent;margin:0;padding:0}body{font-family:var(--font-main);background:var(--bg-gradient);color:var(--text-primary);-webkit-user-select:none;user-select:none;flex-direction:column;align-items:center;min-height:100vh;display:flex;overflow-x:hidden}#root{flex-direction:column;width:100%;max-width:640px;min-height:100vh;padding:16px;display:flex}.header-container,.app-header{border-radius:var(--radius-xl);border:1px solid #e2e8f0;border-top:4px solid var(--bi-red);background:#fff;flex-direction:column;gap:12px;margin-bottom:16px;padding:16px;display:flex;box-shadow:0 10px 25px -5px #0000000d}.header-top,.top-bar{justify-content:space-between;align-items:center;gap:10px;display:flex}.brand-section,.brand{align-items:center;gap:10px;display:flex}.app-logo,.brand-icon{font-size:2.2rem}.app-title{font-size:1.3rem;font-weight:700;line-height:1.2}.app-subtitle{color:var(--text-muted);font-size:.8rem;font-weight:600}.header-right-tools,.stats-group{align-items:center;gap:8px;display:flex}.subject-switcher{background:#f1f5f9;border-radius:16px;gap:4px;padding:3px;display:flex}.subject-btn{font-family:var(--font-main)!important;cursor:pointer!important;border:none!important;border-radius:12px!important;padding:6px 12px!important;font-size:.82rem!important;font-weight:700!important;transition:all .15s!important}.subject-btn.active-bi{box-shadow:0 2px 6px #ef44444d;background:var(--bi-red)!important;color:#fff!important}.subject-btn.active-mandarin{box-shadow:0 2px 6px #0284c74d;background:var(--mandarin-blue)!important;color:#fff!important}.star-badge,.stat-badge{color:#b45309;background:#fffbeb;border:1px solid #fde68a;border-radius:16px;align-items:center;gap:6px;padding:6px 12px;font-size:.9rem;font-weight:700;display:flex}.progress-bar-container,.progress-container{align-items:center;gap:10px;display:flex}.progress-bar-track,.progress-track{background:#e2e8f0;border-radius:8px;flex:1;height:12px;overflow:hidden}.progress-bar-fill,.progress-fill{border-radius:8px;height:100%;transition:width .3s}.progress-text{color:var(--text-muted);white-space:nowrap;font-size:.82rem;font-weight:700}.main-stage{flex-direction:column;flex:1;justify-content:center;align-items:center;width:100%;display:flex}.flashcard-wrapper{width:100%;max-width:560px}.flashcard-container{width:100%;min-height:440px}.card-face{border-radius:var(--radius-xl);background:#fff;border:1.5px solid #e2e8f0;border-bottom:5px solid #cbd5e1;flex-direction:column;justify-content:space-between;width:100%;min-height:440px;padding:24px;animation:.3s ease-in-out fadeIn;display:flex;box-shadow:0 16px 36px -10px #00000014}@keyframes fadeIn{0%{opacity:0;transform:translateY(6px)}to{opacity:1;transform:translateY(0)}}.card-header-bar{justify-content:space-between;align-items:center;width:100%;margin-bottom:8px;display:flex}.category-tag{color:#475569;background:#f1f5f9;border-radius:12px;padding:6px 14px;font-size:.82rem;font-weight:700}.question-box{border-radius:var(--radius-lg);text-align:center;background:#f8fafc;border:1.5px solid #e2e8f0;margin:12px 0;padding:20px}.question-text{color:var(--text-primary);font-size:1.3rem;font-weight:700;line-height:1.5}.options-grid{grid-template-columns:1fr;gap:10px;width:100%;margin-top:10px;display:grid}@media (width>=480px){.options-grid{grid-template-columns:1fr 1fr}}.option-btn{border-radius:var(--radius-lg);width:100%;min-height:56px;font-family:var(--font-main);color:var(--text-primary);cursor:pointer;text-align:left;background:#fff;border:2px solid #cbd5e1;border-bottom:4px solid #94a3b8;align-items:center;gap:12px;padding:12px 16px;font-size:1.05rem;font-weight:700;transition:all .1s;display:flex}.option-btn:hover{background:#f8fafc;border-color:#64748b}.option-btn:active{border-bottom-width:2px;transform:translateY(2px)}.option-index{color:#475569;background:#f1f5f9;border:1px solid #cbd5e1;border-radius:8px;flex-shrink:0;justify-content:center;align-items:center;width:28px;height:28px;font-size:.9rem;font-weight:700;display:flex}.option-label{flex:1;line-height:1.35}.answer-header{border-radius:var(--radius-md);text-align:center;margin-bottom:12px;padding:12px 16px;font-size:1.1rem;font-weight:700}.answer-header.is-correct{color:#15803d;background:#dcfce7;border:1.5px solid #86efac}.answer-header.is-wrong{color:#b91c1c;background:#fee2e2;border:1.5px solid #fca5a5}.back-content{flex-direction:column;flex:1;gap:12px;display:flex}.back-question-title{color:#334155;font-size:1.15rem;font-weight:700;line-height:1.4}.correct-answer-box{border-radius:var(--radius-md);background:#f0fdf4;border:1.5px solid #bbf7d0;padding:14px 16px}.answer-label{color:#166534;font-size:.85rem;font-weight:700}.answer-text{color:#15803d;margin-top:4px;font-size:1.25rem;font-weight:700}.explanation-box{border-radius:var(--radius-md);background:#f8fafc;border:1.5px solid #e2e8f0;padding:14px 16px}.explanation-label{color:#64748b;font-size:.85rem;font-weight:700}.explanation-text{color:#1e293b;margin-top:4px;font-size:1rem;line-height:1.45}.action-btn,.next-btn{border-radius:var(--radius-lg);color:#fff;width:100%;font-family:var(--font-main);cursor:pointer;background:linear-gradient(135deg,#22c55e 0%,#16a34a 100%);border:none;border-bottom:4px solid #15803d;justify-content:center;align-items:center;gap:8px;margin-top:16px;padding:16px;font-size:1.1rem;font-weight:700;transition:all .15s;display:flex}.action-btn:hover,.next-btn:hover{transform:translateY(-1px)}.action-btn:active,.next-btn:active{border-bottom-width:2px;transform:translateY(2px)}