<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://www.w3schools.cn/lib/bootstrap/3.4.1/css/bootstrap.min.css">
<script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.5.1.min.js"></script>
<script src="https://www.w3schools.cn/lib/bootstrap/3.4.1/js/bootstrap.min.js"></script>
</head>
<body>
<div class="container">
<h2>下拉菜单</h2>
<p>.disabled 类用于禁用下拉菜单中的项目：</p>
<div class="dropdown">
<button class="btn btn-default dropdown-toggle" type="button" data-toggle="dropdown">教程
<span class="caret"></span></button>
<ul class="dropdown-menu">
<li><a href="#">HTML</a></li>
<li class="disabled"><a href="#">CSS</a></li>
<li><a href="#">JavaScript</a></li>
</ul>
</div>
</div>
</body>
</html>