选择下拉菜单显示和隐藏的实现

<html>
    <head>
        <meta charset="UTF-8">
        <title></title>
        <style type="text/css">
            .menu:hover .menucontent{
                display: block;
            }
            .menucontent{
                 120px;
                display: none;
                text-align: center;
                border: 1px solid #ddd;
            }
            .menu .btn{
                display: block;
                 50px;
                height: 20px;
                text-align: center;
                font-size: 14px;
                background: red;
                color: #fff;
            }
            
        </style>
    </head>
    <body>
        <div class="menu">
            <span class="btn">菜单</span>
            <div class="menucontent">
                <p>hello</p>
                <p>world</p>
                <p>helloWorld</p>
            </div>
            
        </div>
    </body>
</html>