代码如下
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Navbar Demo</title>
<link href="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/css/bootstrap.min.css" rel="stylesheet">
</head>
<body>
<div class="navbar navbar-default">
<div class="navbar-header">
<button data-toggle="collapse" data-target="#navbar-menu" class="navbar-toggle collapsed">
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a href="#" class="navbar-brand">Brand</a>
</div>
<div id="navbar-menu" class="navbar-collapse collapse">
<ul class="nav navbar-nav">
<li><a href="#">Home</a></li>
<li><a href="#">Download</a></li>
<li><a href="#">Document</a></li>
</ul>
</div>
</div>
<div class="container">
123
</div>
<script src="https://cdn.jsdelivr.net/npm/jquery@1.12.4/dist/jquery.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/js/bootstrap.min.js"></script>
</body>
</html>