/* 额外样式增强 */
.video-card { cursor: pointer; }
.video-card:hover h3 a { color: #667eea; }
.back-to-top { position: fixed; bottom: 2rem; right: 2rem; background: #667eea; color: white; width: 50px; height: 50px; border-radius: 50%; display: flex; align-items: center; justify-content: center; cursor: pointer; opacity: 0; transition: opacity 0.3s; }
.back-to-top.show { opacity: 1; }
@media (max-width: 768px) {
  main { padding: 0 0.5rem; margin: 1rem auto; }
  h1 { font-size: 1.4rem; }
  .video-grid { grid-template-columns: 1fr; gap: 1rem; }
  .detail-container { padding: 1rem; }
}