源代码
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<div class="box">
<label for="cd">主菜单</label>
<input type="checkbox" id="cd" checked>
<ul>
<li>1</li>
<li>2</li>
<li>3</li>
<li>4</li>
<li>5</li>
</ul>
</div>
</body>
</html>
<style>
.box>#cd,#cd+*{display: none;}
.box>#cd:checked+*{display: block;}
</style>