让导航条固定在顶部给body设置了padding-top：70px 为啥还是会遮住内容呢？请大家复制我的代码帮我看一下谢谢了
<!DOCTYPE html>
<html>
<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>现代浏览器博物馆</title>
<!-- Bootstrap -->
<link href="css/bootstrap.min.css" rel="stylesheet">
<!--[if lt IE 9]>
<script src="js/html5shiv.js"></script>
<script src="js/respond.min.js"></script>
<![endif]-->
<style>
body{
padding-top:70px;
}
</style>
</head>
<body>
<nav class="navbar navbar-inverse navbar-fixed-top" role="navigation">
<div>
<!-- Brand and toggle get grouped for better mobile display -->
<div>
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1">
<span>Toggle navigation</span>
<span></span>
<span></span>
<span></span>
</button>
<a href="#">现代浏览器博物馆</a>
</div>
<!-- Collect the nav links, forms, and other content for toggling -->
<div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
<ul class="nav navbar-nav">
<li><a href="#">综述</a></li>
<li><a href="#">简述</a></li>
<li>
<a href="#" data-toggle="dropdown">特点 <span></span></a>
<ul role="menu">
<li><a href="#feature-tab" data-tab="tab-chrome">Chrome</a></li>
<li><a href="#feature-tab" data-tab="tab-firefox">Firefox</a></li>
<li><a href="#feature-tab" data-tab="tab-safari">Safari</a></li>
<li><a href="#feature-tab" data-tab="tab-opera">Opera</a></li>
<li><a href="#feature-tab" data-tab="tab-ie">IE</a></li>
</ul>
</li>
<li><a href="#">关于</a></li>
</ul>
</div><!-- /.navbar-collapse -->
</div><!-- /.container-fluid -->
</nav>
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<!-- jQuery (necessary for Bootstrap's JavaScript plugins) -->
<script src="js/jquery-1.11.1.min.js"></script>
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<script src="js/bootstrap.min.js"></script>
</body>
</html>
