/* ── Responsive: mobile view (≤600px) ── */
@media (max-width: 600px) {
  body { position: relative; overflow: hidden; }

  #sidebar {
    position: absolute; top: 0; left: 0; right: 0; bottom: 0;
    width: 100%; z-index: 10;
    border-right: none; padding: 12px 10px;
    overflow-y: auto;
  }
  body.mobile-chat #sidebar { display: none; }

  #main {
    position: absolute; top: 0; left: 0; right: 0; bottom: 0;
    z-index: 5;
    display: none;
    flex-direction: column; overflow: hidden;
  }
  body.mobile-chat #main { display: flex; }

  #chat-header {
    flex-shrink: 0;
    padding: 10px 12px !important;
  }

  #chat-area { flex: 1; min-height: 0; overflow: hidden; display: flex; flex-direction: column; }
  #inbox { overflow-y: auto; min-height: 0; padding: 10px 12px; }

  #send-area {
    flex-shrink: 0;
    padding: 8px 12px 12px;
    padding-bottom: max(12px, env(safe-area-inset-bottom));
  }

  #btn-back {
    display: flex; align-items: center; justify-content: center;
    background: none; border: none; color: #9cdcfe;
    font-size: 20px; padding: 0 8px 0 0; margin: 0;
    cursor: pointer; flex-shrink: 0; line-height: 1;
  }
  #btn-back:hover { color: #4ec9b0; background: none; }

  .msg { width: 85%; }

  /* Full-screen popups */
  .modal-overlay { align-items: flex-start; }
  .modal {
    width: 100% !important; max-width: 100% !important;
    min-height: 100dvh; border-radius: 0 !important;
    border-left: none; border-right: none;
    padding: 56px 16px 24px !important;
    overflow-y: auto; max-height: 100dvh;
    box-sizing: border-box;
  }
  .modal-close-btn { display: flex; }
}

/* ── Desktop: back button hidden ── */
@media (min-width: 601px) {
  #btn-back { display: none; }
}