/* 扩展样式 */
.video-card { transition: all 0.3s ease; }
.video-card:hover { border-color: #0066cc; }
.video-list li:hover { background: #f0f8ff; }
footer { text-align: center; padding: 2rem; color: #999; margin-top: 3rem; }
@media (max-width: 768px) {
  .video-grid { grid-template-columns: 1fr; }
  .main-title { font-size: 1.5rem; }
  .section { padding: 1.5rem; }
}