* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", sans-serif;
  background: #f3f4f6;
  color: #111827;
}
.app {
  max-width: 1100px;
  margin: 18px auto;
  background: #fff;
  border-radius: 12px;
  overflow: hidden;
  box-shadow: 0 8px 24px rgba(0,0,0,.08);
  display: grid;
  grid-template-columns: 280px 1fr;
  min-height: 78vh;
}
.sidebar {
  border-right: 1px solid #e5e7eb;
  padding: 12px;
  background: #fafafa;
}
.brand { font-size: 20px; font-weight: 700; margin-bottom: 8px; }
.online { font-size: 13px; color: #6b7280; margin-bottom: 10px; }
.section-title { font-size: 13px; color: #6b7280; margin: 12px 0 8px; }
.list { list-style: none; margin: 0; padding: 0; display: flex; flex-direction: column; gap: 6px; }
.list button, .nav-btn {
  width: 100%; text-align: left; border: none; border-radius: 8px;
  padding: 8px 10px; cursor: pointer; background: #e5e7eb;
}
.list button.active, .nav-btn.active { background: #4f46e5; color: #fff; }
.create-row { display: grid; grid-template-columns: 1fr auto; gap: 6px; margin-bottom: 8px; }
input {
  width: 100%; padding: 10px; border: 1px solid #d1d5db; border-radius: 8px; font-size: 14px;
}
button {
  border: none; border-radius: 8px; background: #4f46e5; color: #fff; padding: 10px 12px; cursor: pointer;
}
button:hover { background: #4338ca; }
.main { display: grid; grid-template-rows: auto 1fr auto; }
.chat-header {
  display: flex; justify-content: space-between; align-items: center;
  padding: 12px 14px; border-bottom: 1px solid #e5e7eb;
}
.header-actions { display: flex; align-items: center; gap: 8px; }
.messages {
  list-style: none; margin: 0; padding: 12px; overflow-y: auto; max-height: 62vh;
  display: flex; flex-direction: column; gap: 8px; background: #f9fafb;
}
.message { background: #fff; border: 1px solid #e5e7eb; border-radius: 10px; padding: 10px; }
.meta { color: #6b7280; font-size: 12px; margin-bottom: 4px; display:flex; justify-content:space-between; gap:8px; }
.system { color: #6b7280; font-size: 13px; text-align: center; }
.chat-form, .auth-form { display: flex; gap: 8px; padding: 10px; border-top: 1px solid #e5e7eb; }
.auth-panel { border-top: 1px solid #e5e7eb; }
.tabs { display: flex; gap: 8px; padding: 10px; }
.tab { background: #e5e7eb; color: #111827; }
.tab.active { background: #4f46e5; color: #fff; }
.tip { margin: 0; padding: 0 12px 10px; font-size: 13px; color: #6b7280; }
.hidden { display: none !important; }
.danger { background: #dc2626; }
.danger:hover { background: #b91c1c; }
.msg-del-btn {
  font-size: 12px;
  padding: 2px 8px;
  background: #ef4444;
}
.msg-del-btn:hover { background: #dc2626; }

@media (max-width: 860px) {
  .app { grid-template-columns: 1fr; }
  .sidebar { border-right: none; border-bottom: 1px solid #e5e7eb; }
}