css垂直树形下拉菜单

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS Vertical Tree Menu</title>
    <style>
        ul {
            list-style-type: none;
            padding: 0;
        }
        ul li {
            padding: 8px;
            background-color: #f1f1f1;
            border-bottom: 1px solid #ddd;
        }
        ul li:hover {
            background-color: #ddd;
        }
        ul li ul {
            display: none;
            padding-left: 20px;
        }
        ul li:hover > ul {
            display: block;
        }
    </style>
</head>
<body>
    <ul>
        <li>Menu Item 1
            <ul>
                <li>Sub Item 1.1</li>
                <li>Sub Item 1.2</li>
            </ul>
        </li>
        <li>Menu Item 2
            <ul>
                <li>Sub Item 2.1</li>
                <li>Sub Item 2.2
                    <ul>
                        <li>Sub Item 2.2.1</li>
                        <li>Sub Item 2.2.2</li>
                    </ul>
                </li>
            </ul>
        </li>
    </ul>
</body>
</html>