我这个怎么实现不了导航条呢
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="css/bootstrap.min.css">
<title>后台管理系统</title>
</head>
<body>
<nav class="navbar navbar-default navbar-fixed-top navbar-inverse" role="navigation">
<div class="container">
<div class="navbar-header">
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
<span class="sr-only">切换导航</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand" href="#">首页</a>
</div>
<div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
<ul class="nav navbar-nav">
<li class="active"><a href="#">iOS</a></li>
<li><a href="#">SVN</a></li>
</ul>
</div>
</div>
</nav>
<script src="js/jquery-3.4.1.js"></script>
<script src="js/bootstrap.min.js"></script>
</body>
</html>
