:root {
  --bg: #ffffff;
  --bg-sidebar: #f4f5f7;
  --bg-hover: #e8eaee;
  --bg-active: #2f6fed;
  --fg: #1d2129;
  --fg-muted: #6b7280;
  --fg-on-active: #ffffff;
  --border: #e2e5ea;
  --accent: #2f6fed;
  --danger: #d0342c;
  --online: #22a55a;
  font-family: system-ui, -apple-system, "Hiragino Sans", "Noto Sans JP", sans-serif;
  color-scheme: light dark;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #1b1d22;
    --bg-sidebar: #15171b;
    --bg-hover: #262a31;
    --bg-active: #3b73e8;
    --fg: #e6e8eb;
    --fg-muted: #9aa1ad;
    --border: #2b2f36;
    --accent: #6d9bff;
    --danger: #ff6b61;
  }
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }
html, body { height: 100%; margin: 0; }
body { background: var(--bg); color: var(--fg); font-size: 15px; }
button, input, textarea { font: inherit; color: inherit; }

.layout { display: grid; grid-template-columns: 260px 1fr; height: 100dvh; }

/* サイドバー */
.sidebar { background: var(--bg-sidebar); border-right: 1px solid var(--border); overflow-y: auto; padding-bottom: 16px; }
.sidebar-header { display: flex; align-items: center; justify-content: space-between; gap: 8px; padding: 16px; border-bottom: 1px solid var(--border); }
.brand { font-weight: 700; font-size: 17px; }
.me { background: none; border: 1px solid var(--border); border-radius: 999px; padding: 2px 10px; font-size: 13px; cursor: pointer; max-width: 120px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.me:hover { background: var(--bg-hover); }
.sidebar h2 { font-size: 12px; font-weight: 600; text-transform: uppercase; letter-spacing: .04em; color: var(--fg-muted); margin: 20px 16px 6px; }
.count { font-weight: 400; }
.channel-list, .online-list { list-style: none; margin: 0; padding: 0 8px; }
.channel-list button { display: flex; width: 100%; align-items: center; justify-content: space-between; gap: 8px; border: 0; background: none; text-align: left; padding: 6px 8px; border-radius: 6px; cursor: pointer; }
.channel-list button:hover { background: var(--bg-hover); }
.channel-list button[aria-current="true"] { background: var(--bg-active); color: var(--fg-on-active); }
.channel-list .unread { font-weight: 700; }
.badge { background: var(--danger); color: #fff; border-radius: 999px; font-size: 11px; padding: 0 6px; min-width: 18px; text-align: center; }
.channel-form { padding: 4px 8px; }
.channel-form input { width: 100%; border: 1px dashed var(--border); background: transparent; border-radius: 6px; padding: 6px 8px; }
.channel-form input:focus { outline: 2px solid var(--accent); border-color: transparent; }
.online-list li { display: flex; align-items: center; gap: 8px; padding: 4px 8px; }
.online-list li::before { content: ""; width: 8px; height: 8px; border-radius: 50%; background: var(--online); flex: none; }

/* チャット */
.chat { display: flex; flex-direction: column; min-width: 0; min-height: 0; }
.chat-header { display: flex; align-items: center; gap: 12px; padding: 12px 20px; border-bottom: 1px solid var(--border); }
.chat-header h1 { font-size: 17px; margin: 0; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.menu { display: none; border: 0; background: none; font-size: 20px; cursor: pointer; padding: 0 4px; }
.status { margin-left: auto; font-size: 12px; color: var(--danger); }
.messages { flex: 1; overflow-y: auto; padding: 12px 0; }
.load-older { display: block; margin: 0 auto 12px; border: 1px solid var(--border); background: none; border-radius: 999px; padding: 4px 14px; font-size: 13px; cursor: pointer; color: var(--fg-muted); }
.message-list { list-style: none; margin: 0; padding: 0; }
.message { padding: 2px 20px; }
.message:hover { background: var(--bg-hover); }
.message.first { margin-top: 10px; }
.message-meta { display: flex; align-items: baseline; gap: 8px; }
.author { font-weight: 700; }
.time { font-size: 12px; color: var(--fg-muted); }
.body { white-space: pre-wrap; overflow-wrap: anywhere; line-height: 1.5; }
.day-divider { display: flex; align-items: center; gap: 12px; margin: 16px 20px 4px; font-size: 12px; color: var(--fg-muted); }
.day-divider::before, .day-divider::after { content: ""; flex: 1; border-top: 1px solid var(--border); }
.empty { text-align: center; color: var(--fg-muted); padding: 40px 20px; }

.composer { display: flex; gap: 8px; padding: 12px 20px 16px; border-top: 1px solid var(--border); }
.composer textarea { flex: 1; resize: none; border: 1px solid var(--border); border-radius: 8px; padding: 10px 12px; background: var(--bg); max-height: 200px; line-height: 1.4; }
.composer textarea:focus { outline: 2px solid var(--accent); border-color: transparent; }
.composer button, #login-form button { border: 0; background: var(--accent); color: #fff; border-radius: 8px; padding: 0 18px; cursor: pointer; font-weight: 600; }
.composer button:disabled { opacity: .5; cursor: default; }
.error { margin: 0 20px 12px; color: var(--danger); font-size: 13px; }

/* ログイン */
dialog { border: 1px solid var(--border); border-radius: 12px; padding: 28px; background: var(--bg); color: var(--fg); width: min(360px, calc(100vw - 32px)); }
dialog::backdrop { background: rgb(0 0 0 / .4); }
#login-form { display: grid; gap: 10px; }
#login-form h1 { margin: 0 0 8px; font-size: 20px; }
#login-form label { font-size: 13px; color: var(--fg-muted); }
#login-form input { border: 1px solid var(--border); border-radius: 8px; padding: 10px 12px; background: var(--bg); }
#login-form button { padding: 10px; margin-top: 6px; }

/* モバイル */
@media (max-width: 720px) {
  .layout { grid-template-columns: 1fr; }
  .sidebar { position: fixed; inset: 0 auto 0 0; width: min(280px, 85vw); z-index: 10; transform: translateX(-100%); transition: transform .2s; }
  .sidebar.open { transform: none; box-shadow: 0 0 0 100vmax rgb(0 0 0 / .35); }
  .menu { display: block; }
  .chat-header, .composer { padding-left: 16px; padding-right: 16px; }
  .message { padding: 2px 16px; }
}