/* --- 左侧边栏 --- */
        .sidebar {
            width: 260px;
            border-right: 1px solid var(--border-light);
            display: flex;
            flex-direction: column;
            padding: 24px 16px;
            transition: width 0.3s ease, padding 0.3s ease, opacity 0.2s ease;
            overflow: hidden;
            flex-shrink: 0;
            background-color: var(--bg-sidebar);
        }
        .sidebar.hidden { width: 0; padding-left: 0; padding-right: 0; opacity: 0; border-right: none; }

        .sidebar-brand { display: flex; align-items: center; gap: 8px; font-size: 14px; margin-bottom: 32px; padding: 0 4px; white-space: nowrap; }
        .sidebar-brand strong { font-weight: 700; }
        .sidebar-brand span { color: var(--text-muted); }

        .sidebar-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 16px; padding: 0 4px; white-space: nowrap; }
        .sidebar-header h2 { font-size: 16px; font-weight: 600; color: var(--text-main); margin: 0; }
        .sidebar-actions { display: flex; align-items: center; gap: 12px; color: var(--text-muted); }
        .sidebar-actions svg { width: 16px; height: 16px; opacity: 0.65; cursor: pointer; transition: all 0.2s ease; }
        .sidebar-actions svg:hover { opacity: 1; color: var(--text-main); transform: scale(1.08); }

        .chat-list { flex: 1; overflow-y: auto; display: flex; flex-direction: column; gap: 4px; }
        .chat-history-item { display: flex; align-items: center; gap: 10px; padding: 8px 12px; border-radius: 8px; font-size: 14px; cursor: pointer; color: var(--text-muted); transition: all 0.2s ease; white-space: nowrap; overflow: hidden; }
        .chat-history-item:hover { background-color: var(--bg-hover); color: var(--text-main); }
        .chat-history-item.active { background-color: var(--bg-active-chat); color: var(--text-main); }
        .chat-history-item.selected { background-color: var(--bg-active-chat); color: var(--text-main); }
        .chat-title { white-space: nowrap; overflow: hidden; text-overflow: ellipsis; flex: 1; }
        
        /* 多选 checkbox */
        .chat-checkbox { width: 16px; height: 16px; border: 2px solid var(--border-color); border-radius: 4px; flex-shrink: 0; display: none; align-items: center; justify-content: center; transition: all 0.15s; }
        .multi-select-mode .chat-checkbox { display: flex; }
        .multi-select-mode .chat-history-item { padding-left: 12px; }
        .chat-checkbox.checked { background: var(--black-btn); border-color: var(--black-btn); }
        .chat-checkbox.checked::after { content: ''; width: 4px; height: 8px; border: solid var(--text-on-dark); border-width: 0 2px 2px 0; transform: rotate(45deg); margin-bottom: 2px; }
        
        /* 多选操作栏 */
        .multi-select-bar {
            display: none;
            flex-direction: column;
            gap: 6px;
            padding: 8px 10px;
            background: var(--bg-hover);
            border-radius: 8px;
            margin-bottom: 8px;
            border: 1px solid var(--border-light);
        }
        .multi-select-bar.show {
            display: flex;
        }
        .ms-row-top {
            display: flex;
            justify-content: space-between;
            align-items: center;
            width: 100%;
        }
        .ms-row-top .ms-actions-right {
            display: flex;
            gap: 6px;
        }
        .ms-row-bottom {
            display: flex;
            gap: 6px;
            width: 100%;
        }
        .multi-select-bar .ms-count {
            font-size: 11px;
            color: var(--text-muted);
            font-weight: 500;
        }
        .multi-select-bar .ms-btn {
            font-size: 11px;
            padding: 4px 8px;
            border-radius: 6px;
            border: 1px solid var(--border-color);
            background: var(--bg-surface);
            color: var(--text-muted);
            cursor: pointer;
            transition: all 0.15s ease;
            white-space: nowrap;
            display: inline-flex;
            align-items: center;
            justify-content: center;
        }
        .ms-row-bottom .ms-btn {
            flex: 1;
        }
        .multi-select-bar .ms-btn:hover {
            color: var(--text-main);
            border-color: var(--text-main);
            background: var(--bg-hover);
        }
        .multi-select-bar .ms-btn.danger:hover {
            color: #ff4d4f;
            border-color: #ff4d4f;
            background: #fff1f0;
        }
        .dark-mode .multi-select-bar .ms-btn.danger:hover {
            color: #ff7875;
            border-color: #ff7875;
            background: #2a1215;
        }
        
        .chat-history-icons {
            display: none;
            align-items: center;
            gap: 8px;
            color: var(--text-muted);
            flex-shrink: 0;
            margin-left: 6px;
        }
        .chat-history-icons div {
            display: flex;
            align-items: center;
            justify-content: center;
            padding: 4px;
            border-radius: 4px;
            transition: all 0.15s ease;
        }
        .chat-history-icons div:hover {
            background-color: var(--bg-hover);
            color: var(--text-main);
        }
        .chat-history-item:hover .chat-history-icons, .chat-history-item.active .chat-history-icons { display: flex; }

        /* --- 右侧主体 --- */
        .main-content {
            flex: 1;
            display: flex;
            flex-direction: column;
            position: relative;
            min-width: 0;
        }

        .top-nav {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 16px 24px;
            min-height: 60px;
            z-index: 10;
        }

        .nav-left-actions { display: flex; align-items: center; color: var(--text-main); cursor: pointer; }
        .sidebar-toggle-btn { display: none; opacity: 0.7; transition: opacity 0.2s; }
        .sidebar-toggle-btn:hover { opacity: 1; }

        .settings-btn {
            background: none;
            border: 1px solid var(--border-color);
            padding: 6px 12px;
            border-radius: 12px;
            cursor: pointer;
            color: var(--text-muted);
            font-size: 13px;
            transition: all 0.2s;
        }
        .settings-btn:hover { color: var(--text-main); border-color: var(--text-muted); }

        .nav-right-actions {
            display: flex;
            align-items: center;
            gap: 8px;
            margin-left: auto;
        }

        .dark-mode-btn {
            background: none;
            border: none;
            cursor: pointer;
            color: var(--text-muted);
            padding: 6px;
            display: flex;
            align-items: center;
            justify-content: center;
            border-radius: 8px;
            transition: all 0.2s;
        }
        .dark-mode-btn:hover {
            color: var(--text-main);
            background-color: var(--bg-hover);
        }