HTML+CSS 速成10分钟！一键实现你的后台管理系统首页梦想！

<div class="container">
        <nav class="sidebar">
            <h2>管理菜单</h2>
            <ul>
                <li class="menu-item">
                    <a href="#dashboard">仪表板</a>
                </li>
                <li class="menu-item active">
                    <a href="#users">用户管理</a>
                    <ul class="submenu">
                        <li><a href="#user-list">用户列表</a></li>
                        <li><a href="#user-roles">角色管理</a></li>
                        <li><a href="#user-permissions">权限设置</a></li>
                    </ul>
                </li>
                <li class="menu-item">
                    <a href="#products">产品管理</a>
                    <ul class="submenu">
                        <li><a href="#product-list">产品列表</a></li>
                        <li><a href="#product-categories">分类管理</a></li>
                        <li><a href="#product-inventory">库存管理</a></li>
                    </ul>
                </li>
                <li class="menu-item">
                    <a href="#orders">订单管理</a>
                    <ul class="submenu">
                        <li><a href="#order-list">订单列表</a></li>
                        <li><a href="#order-processing">订单处理</a></li>
                        <li><a href="#order-returns">退货管理</a></li>
                    </ul>
                </li>
                <li class="menu-item">
                    <a href="#settings">系统设置</a>
                    <ul class="submenu">
                        <li><a href="#general-settings">常规设置</a></li>
                        <li><a href="#security-settings">安全设置</a></li>
                        <li><a href="#backup-restore">备份与恢复</a></li>
                    </ul>
                </li>
            </ul>
        </nav>
        <main class="main-content">
            <header class="header">
                <h1>后台管理系统</h1>
                <span>欢迎回来，管理员</span>
            </header>
            <section class="welcome-guide">
                <h1>欢迎使用后台管理系统</h1>
                <p>这里是您管理整个系统的中心。您可以轻松地查看统计数据、管理用户、处理订单，以及执行更多操作。如果您需要任何帮助，请随时查看我们的帮助文档或联系技术支持团队。</p>
                <a href="#" class="btn">开始使用</a>
            </section>
        </main>
    </div>

:root {
            --primary-color: #3498db;
            --secondary-color: #2c3e50;
            --background-color: #f5f7fa;
            --text-color: #333;
            --sidebar-width: 240px;
        }
        body, html {
            margin: 0;
            padding: 0;
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            height: 100%;
            background-color: var(--background-color);
            color: var(--text-color);
        }
        .container {
            display: flex;
            height: 100%;
        }
        .sidebar {
            width: var(--sidebar-width);
            background-color: var(--secondary-color);
            color: white;
            padding: 20px 0;
            overflow-y: auto;
        }
        .sidebar h2 {
            margin: 0;
            padding: 0 20px 20px;
            font-size: 1.2em;
            border-bottom: 1px solid rgba(255,255,255,0.1);
        }
        .sidebar ul {
            list-style-type: none;
            padding: 0;
            margin: 0;
        }
        .sidebar ul li {
            margin: 0;
        }
        .sidebar ul li a {
            color: white;
            text-decoration: none;
            padding: 12px 20px;
            display: block;
            transition: background-color 0.3s;
        }
        .sidebar ul li a:hover {
            background-color: rgba(255,255,255,0.1);
        }
        .sidebar .submenu {
            background-color: rgba(0,0,0,0.1);
            overflow: hidden;
            max-height: 0;
            transition: max-height 0.3s ease-out;
        }
        .sidebar .submenu a {
            padding-left: 40px;
        }
        .sidebar .menu-item.active .submenu {
            max-height: 500px;
        }
        .sidebar .menu-item > a::after {
            content: '▼';
            float: right;
            transform: rotate(-90deg);
            transition: transform 0.3s;
        }
        .sidebar .menu-item.active > a::after {
            transform: rotate(0);
        }
        .main-content {
            flex-grow: 1;
            display: flex;
            flex-direction: column;
        }
        .header {
            background-color: white;
            color: var(--text-color);
            padding: 15px 30px;
            display: flex;
            justify-content: space-between;
            align-items: center;
            box-shadow: 0 2px 5px rgba(0,0,0,0.1);
        }
        .header h1{padding: 0; margin: 0;}
        .welcome-guide {
            padding: 40px;
            text-align: center;
            flex-grow: 1;
            display: flex;
            flex-direction: column;
            justify-content: center;
            align-items: center;
        }
        .welcome-guide h1 {
            color: var(--primary-color);
            margin-bottom: 20px;
            font-size: 2.5em;
        }
        .welcome-guide p {
            max-width: 600px;
            margin-bottom: 30px;
            line-height: 1.6;
        }
        .btn {
            background-color: var(--primary-color);
            color: white;
            padding: 12px 24px;
            text-decoration: none;
            border-radius: 5px;
            transition: background-color 0.3s, transform 0.3s;
            font-weight: bold;
        }
        .btn:hover {
            background-color: #2980b9;
            transform: translateY(-2px);
        }

<script>
        document.querySelectorAll('.menu-item > a').forEach(item => {
            item.addEventListener('click', (e) => {
                e.preventDefault();
                const parent = item.parentElement;
                parent.classList.toggle('active');
            });
        });
    </script>