/* ============ 移动端适配 ============ */
@media (max-width: 900px) {
  .app { flex-direction: column; }
  .sidebar {
    width: 100%; height: auto; position: static; flex-direction: row;
    align-items: center; padding: 8px 12px; flex-wrap: wrap;
  }
  .brand { border-bottom: none; padding: 8px; }
  .brand span { display: none; }
  .nav { flex-direction: row; padding: 4px; overflow-x: auto; }
  .nav-item { padding: 8px 10px; }
  .nav-item span { display: none; }
  .sidebar-footer { border-top: none; padding: 4px; }
  .content { padding: 14px; }
  .page-head h2 { font-size: 17px; }
  .stat-grid { grid-template-columns: repeat(2, 1fr); }
  .card-list { grid-template-columns: 1fr; }
  .log-list { height: 60vh; }
  .form-grid { grid-template-columns: 1fr; }
  .modal { width: 100%; }
}