/* 教学前端浅色主题，Apple 风格 */
:root {
  --bg-primary: #F5F5F7;
  --bg-card: #FFFFFF;
  --text-primary: #1D1D1F;
  --text-secondary: #86868B;
  --accent: #0071E3;
  --border: #D2D2D7;
  --success: #34C759;
  --warning: #FF9500;
  --danger: #FF3B30;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: -apple-system, "PingFang SC", "Microsoft YaHei", sans-serif; background: var(--bg-primary); color: var(--text-primary); }
.app { display: flex; flex-direction: column; height: 100vh; }

.topbar { display: flex; align-items: center; gap: 24px; padding: 0 24px; height: 56px; background: var(--bg-card); border-bottom: 1px solid var(--border); }
.brand { font-size: 18px; font-weight: 600; }
.brand span { color: var(--text-secondary); font-weight: 400; margin-left: 6px; }
.quota-bar { display: flex; align-items: center; gap: 10px; flex: 1; max-width: 480px; }
.quota-label { color: var(--text-secondary); font-size: 13px; }
.quota-value { font-size: 13px; font-weight: 500; }
.quota-progress { flex: 1; height: 6px; background: var(--border); border-radius: 3px; overflow: hidden; }
.quota-progress-fill { height: 100%; background: var(--accent); transition: width .3s; }
.quota-remaining { color: var(--text-secondary); font-size: 13px; }
.btn-refresh { background: none; border: 1px solid var(--border); border-radius: 6px; padding: 3px 10px; cursor: pointer; font-size: 12px; color: var(--text-secondary); }
.user-area { margin-left: auto; font-size: 13px; color: var(--text-secondary); }

.main { display: flex; flex: 1; overflow: hidden; }
.sidebar { width: 180px; background: var(--bg-card); border-right: 1px solid var(--border); padding: 12px 8px; overflow-y: auto; }
.nav-item { display: block; padding: 9px 14px; border-radius: 8px; color: var(--text-primary); text-decoration: none; font-size: 14px; cursor: pointer; }
.nav-item:hover { background: var(--bg-primary); }
.nav-item.active { background: var(--accent); color: #fff; }
.nav-divider { height: 1px; background: var(--border); margin: 8px 12px; }
.content { flex: 1; }
.content iframe { width: 100%; height: 100%; border: none; }

.footer { display: flex; align-items: center; gap: 16px; padding: 0 24px; height: 40px; background: var(--bg-card); border-top: 1px solid var(--border); font-size: 12px; color: var(--text-secondary); }
.footer a { color: var(--text-secondary); text-decoration: none; }
.footer a:hover { color: var(--accent); }

.modal { display: none; position: fixed; inset: 0; background: rgba(0,0,0,.4); align-items: center; justify-content: center; z-index: 100; }
.modal.show { display: flex; }
.modal-box { background: var(--bg-card); border-radius: 12px; padding: 24px; width: 360px; }
.modal-box h3 { margin-bottom: 12px; }
.modal-sub { color: var(--text-secondary); font-size: 13px; margin-top: 6px; }
.modal-actions { display: flex; justify-content: flex-end; gap: 10px; margin-top: 20px; }
.btn-cancel, .btn-confirm { padding: 7px 18px; border-radius: 8px; border: none; cursor: pointer; font-size: 14px; }
.btn-cancel { background: var(--bg-primary); color: var(--text-primary); }
.btn-confirm { background: var(--accent); color: #fff; }