*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}body{font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,Oxygen,Ubuntu,Cantarell,sans-serif;line-height:1.6;color:#333;background:#f5f7fa;-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale}a{color:#2563eb;text-decoration:none}a:hover{text-decoration:underline}.container{width:100%;max-width:1200px;margin:0 auto;padding:0 16px}@media(min-width:768px){.container{padding:0 24px}}.breadcrumb{display:flex;flex-wrap:wrap;gap:8px;padding:12px 0;font-size:14px;list-style:none;overflow-x:auto;white-space:nowrap;-webkit-overflow-scrolling:touch}.breadcrumb li{display:inline-flex;align-items:center}.breadcrumb li+li::before{content:'›';margin:0 8px;color:#64748b}.breadcrumb a{color:#64748b}.breadcrumb .active{color:#333}.topic-header{background:#fff;padding:20px 0;border-bottom:1px solid #e2e8f0;margin-bottom:20px}@media(min-width:768px){.topic-header{padding:32px 0}}.topic-meta-info{display:flex;flex-wrap:wrap;gap:12px;margin-bottom:12px;font-size:14px}.topic-tag{background:#dbeafe;color:#1e40af;padding:4px 12px;border-radius:16px;font-weight:500}.topic-date{color:#64748b}.topic-title{font-size:24px;font-weight:700;line-height:1.3;margin-bottom:16px;color:#1e293b}@media(min-width:768px){.topic-title{font-size:32px}}.topic-stats-header{display:flex;flex-wrap:wrap;gap:16px;font-size:14px;color:#64748b}.topic-stats-header span{display:flex;align-items:center;gap:4px}.section{background:#fff;padding:20px 0;margin-bottom:20px}@media(min-width:768px){.section{padding:32px 0}}.section-heading{font-size:20px;font-weight:700;margin-bottom:16px;color:#1e293b}@media(min-width:768px){.section-heading{font-size:24px}}.video-container{position:relative;padding-bottom:56.25%;height:0;overflow:hidden;background:#000;border-radius:12px;margin-bottom:16px}.video-container iframe{position:absolute;top:0;left:0;width:100%;height:100%;border:0}.video-tips{background:#f8fafc;border-left:4px solid #2563eb;padding:16px;border-radius:8px;font-size:14px}.video-tips p{font-weight:600;margin-bottom:8px}.video-tips ul{margin-left:20px;margin-top:8px}.video-tips li{margin-bottom:4px}.topic-content{background:#fff;padding:20px;border-radius:12px;font-size:16px;line-height:1.8}@media(min-width:768px){.topic-content{padding:32px;font-size:17px}}.topic-content p{margin-bottom:16px}.quiz-wrapper{background:#fff;padding:20px;border-radius:12px}@media(min-width:768px){.quiz-wrapper{padding:32px}}.quiz-header{text-align:center;margin-bottom:24px}.quiz-subtitle{color:#64748b;margin:8px 0 16px}.quiz-stats{display:flex;flex-wrap:wrap;justify-content:center;gap:12px;margin-top:16px}.stat-badge{background:#f1f5f9;padding:8px 16px;border-radius:20px;font-size:14px;font-weight:500}.quiz-question{background:#f8fafc;padding:20px;border-radius:12px;margin-bottom:20px;border:2px solid transparent;transition:all .3s}.quiz-question.correct{border-color:#10b981;background:#ecfdf5}.quiz-question.incorrect{border-color:#ef4444;background:#fef2f2}.question-text{font-size:16px;font-weight:600;margin-bottom:16px;line-height:1.5}@media(min-width:768px){.question-text{font-size:18px}}.question-options{display:flex;flex-direction:column;gap:12px}.option-label{display:flex;align-items:center;padding:16px;background:#fff;border:2px solid #e2e8f0;border-radius:8px;cursor:pointer;transition:all .2s;-webkit-tap-highlight-color:transparent}.option-label:hover,.option-label:active{border-color:#2563eb;background:#f0f9ff}.option-label input{margin-right:12px;width:20px;height:20px;cursor:pointer}.option-label span{flex:1;font-size:15px}.btn-start-quiz,.btn-submit-quiz,.btn-retry,.btn-more{display:inline-block;padding:16px 32px;font-size:16px;font-weight:600;border:none;border-radius:8px;cursor:pointer;transition:all .3s;text-align:center;min-height:48px;-webkit-tap-highlight-color:transparent}@media(min-width:768px){.btn-start-quiz,.btn-submit-quiz,.btn-retry,.btn-more{font-size:18px;padding:18px 40px}}.btn-start-quiz{background:#2563eb;color:#fff;width:100%;margin:16px 0}.btn-start-quiz:hover{background:#1d4ed8;text-decoration:none}.btn-submit-quiz{background:#10b981;color:#fff;width:100%;margin-top:16px}.btn-submit-quiz:hover{background:#059669}.quiz-note{text-align:center;color:#64748b;font-size:14px;margin-top:8px}.quiz-results{background:#fff;padding:24px;border-radius:12px;margin-top:24px}.score-display{text-align:center;margin:24px 0;padding:24px;background:linear-gradient(135deg,#667eea 0%,#764ba2 100%);border-radius:12px;color:#fff}.score-number{font-size:48px;font-weight:700;margin-bottom:8px}.score-percentage{font-size:24px;opacity:.9}.explanations-section{margin-top:24px}.explanation-item{padding:16px;margin-bottom:16px;border-radius:8px;border-left:4px solid #e2e8f0}.correct-explanation{background:#ecfdf5;border-left-color:#10b981}.incorrect-explanation{background:#fef2f2;border-left-color:#ef4444}.explanation-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:12px;flex-wrap:wrap;gap:8px}.explanation-status{font-size:14px;font-weight:600}.explanation-text{color:#475569;font-size:14px;margin-top:8px;font-style:italic}.results-actions{display:flex;gap:12px;margin-top:24px;flex-wrap:wrap}.results-actions .btn-retry,.results-actions .btn-more{flex:1;min-width:140px;background:#64748b;color:#fff}.results-actions .btn-retry:hover,.results-actions .btn-more:hover{background:#475569;text-decoration:none}.related-grid{display:grid;grid-template-columns:1fr;gap:16px;margin-top:20px}@media(min-width:640px){.related-grid{grid-template-columns:repeat(2,1fr)}}@media(min-width:1024px){.related-grid{grid-template-columns:repeat(3,1fr)}}.related-card{display:block;background:#fff;padding:20px;border-radius:12px;border:1px solid #e2e8f0;transition:all .3s;-webkit-tap-highlight-color:transparent}.related-card:hover{border-color:#2563eb;box-shadow:0 4px 12px rgba(37,99,235,.1);text-decoration:none;transform:translateY(-2px)}.related-card h3{font-size:16px;font-weight:600;margin-bottom:8px;color:#1e293b}@media(min-width:768px){.related-card h3{font-size:18px}}.related-card p{color:#64748b;font-size:14px;margin-bottom:12px;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden}.related-meta{display:flex;gap:12px;font-size:13px;color:#94a3b8}.btn-lg{padding:16px 48px;font-size:18px;font-weight:600;background:#2563eb;color:#fff;border:none;border-radius:8px;cursor:pointer;transition:all .3s;display:inline-block;min-height:56px;-webkit-tap-highlight-color:transparent}.btn-lg:hover{background:#1d4ed8;text-decoration:none;transform:translateY(-2px);box-shadow:0 4px 12px rgba(37,99,235,.2)}.text-center{text-align:center}.my-4{margin:32px 0}.mb-3{margin-bottom:24px}@media(max-width:640px){.container{padding:0 12px}.topic-header{padding:16px 0}.section{padding:16px 0}.topic-content{padding:16px}.quiz-wrapper{padding:16px}}