@media (max-width: 1080px) {
  .app-shell { grid-template-columns: 220px minmax(0, 1fr); }
  .sidebar.right { display: none; }
}

@media (max-width: 780px) {
  .app-shell { grid-template-columns: 1fr; }
  .sidebar.left { position: static; }
  .messages-layout { grid-template-columns: 1fr; }
  .grid-3, .grid-4 { grid-template-columns: 1fr; }
  .topbar { flex-wrap: wrap; }
}