/* 响应式（从 /style.css 拆分） */
@media (max-width: 640px) {
  .book-grid { grid-template-columns: 1fr; }
  .reader { padding: 20px 16px; }
  .reader-content { font-size: calc(var(--font-size) - 1px); }
  .navbar { padding: 12px 16px; }
  .navbar h1 { font-size: 17px; }
  .navbar nav { gap: 10px; }
  .navbar nav a { font-size: 13px; }
  .container { padding: 16px; }
  .book-header { padding: 16px; }
  .book-header h2 { font-size: 20px; }
  .chapter-list a { padding: 12px 16px; }
  .reader-toolbar { flex-wrap: wrap; gap: 8px; }
  .reader-nav { flex-direction: column; gap: 10px; }
  .reader-nav a, .reader-nav span { text-align: center; width: 100%; }
  .admin-list li { flex-direction: column; align-items: flex-start; gap: 8px; }
  .admin-list .item-actions { width: 100%; }
  .back-to-top { bottom: 20px; right: 20px; width: 38px; height: 38px; font-size: 16px; }
  .reader-bottom-bar { max-width: 100%; }
  .settings-panel { padding: 16px 16px 24px; }
  .back-to-top.has-bar { bottom: 70px; }
}