:root{--primary-color:#2c5aa0;--secondary-color:#f8f9fa;--accent-color:#ff6b35;--text-color:#333;--light-text:#6c757d;--border-color:#dee2e6;--shadow:0 4px 6px rgba(0, 0, 0, 0.1)}body{background-color:#f5f7fa;color:var(--text-color);line-height:1.6}.container{display:flex;max-width:1400px;margin-top:90px;gap:10px}.sidebar{flex:0 0 320px;background:#fff;border-radius:10px;box-shadow:var(--shadow);padding:20px;height:fit-content;min-height:700px}.sidebar h2{color:var(--primary-color);margin-bottom:20px;padding-bottom:10px;border-bottom:2px solid var(--border-color);font-size:1rem}.category-list{list-style:none;padding-inline-start:0}.category-item{margin-bottom:5px}.category-item>a{display:flex;align-items:center;justify-content:space-between;padding:12px 15px;text-decoration:none;color:var(--text-color);border-radius:8px;transition:all 0.3s ease;font-weight:500}.category-item>a:hover{background-color:var(--secondary-color);color:var(--primary-color)}.category-item>a.active{background-color:var(--primary-color);color:#fff}.category-item i{margin-left:10px;font-size:1.1rem}.toggle-icon{transition:transform 0.3s ease}.category-item.active .toggle-icon{transform:rotate(90deg)}.subcategory-link{display:block;padding:7px 15px;text-decoration:none;color:#333;transition:all 0.3s ease;border-radius:6px;margin:2px 0}.subcategory-link:hover{background-color:#f8f9fa}.subcategory-link.active{background-color:#e3f2fd;color:#1976d2}.sub-item-content{display:flex;justify-content:space-between;align-items:center;width:100%}.sub-item-main{display:flex;align-items:center;flex:1;min-width:0}.play-icon{color:#666;margin-left:8px;flex-shrink:0;transition:all 0.3s ease}.sub-item-title{font-size:14px;line-height:1.4;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}.sub-item-time{flex-shrink:0;margin-right:5px}.time-badge{background-color:#f1f3f4;color:#5f6368;padding:4px 8px;border-radius:12px;font-size:11px;font-weight:500;white-space:nowrap}.subcategory-link.active .play-icon{color:#1976d2}.subcategory-link.active .time-badge{background-color:#1976d2;color:#fff}.subcategory-link:hover .play-icon{color:#1976d2;transform:scale(1.1)}.subcategory-list.level-3 .sub-item-content{padding-right:15px}.subcategory-list.level-3 .play-icon{width:14px;height:14px;margin-left:6px}.subcategory-list.level-3 .sub-item-title{font-size:13px}.subcategory-list.level-3 .time-badge{font-size:10px;padding:3px 6px}@media (max-width:768px){.sub-item-content{align-items:flex-start}.sub-item-time{margin-right:0;margin-top:4px}.sub-item-main{width:100%}}.video-content{flex:1;display:flex;flex-direction:column;gap:10px}.video-container{max-width:100%!important;background:#fff;box-shadow:var(--shadow);overflow:hidden}.video-player{width:100%;aspect-ratio:16/9;background-color:#000;display:flex;align-items:center;justify-content:center;color:#fff;font-size:1.2rem}video{border-radius:0px!important}.video-info{padding:20px}.video-title{font-size:1.5rem;margin-bottom:10px;color:var(--primary-color)}.video-description{color:var(--light-text);line-height:1.8}.video-meta{display:flex;justify-content:space-between;margin-top:15px;font-size:.9rem;color:var(--light-text)}footer{background-color:var(--primary-color);color:#fff;text-align:center;padding:20px;margin-top:40px}@media (max-width:992px){.container{flex-direction:column}.sidebar{flex:1}}@media (max-width:768px){.header-content{flex-direction:column;gap:15px}.search-bar{width:100%;max-width:400px}}@media (max-width:576px){.video-meta{flex-direction:column;gap:5px}.sidebar{padding:15px}.category-item>a{padding:10px 12px}.subcategory-item a{padding:8px 12px}}.subcategory-list{display:none;padding-right:20px;border-radius:4px;margin:5px 0}.category-item.active>.subcategory-list{display:block}.category-item.active>a>svg{transform:rotate(180deg)}.category-link>svg{transition:transform 0.3s ease}.category-item.active>a{color:#007bff;font-weight:700}.subcategory-link.active{color:#007bff;font-weight:700;background-color:rgb(0 123 255 / .1)}.subcategory-list.level-3{padding-right:15px;border-right:2px solid #e0e0e0;margin:3px 0}