<title>W3xue教程(w3xue.com)</title>
<link rel="stylesheet" href="/css/bootstrap/bootstrap3.3.7.min.css">
<script src="/js/bootstrap/jquery.min.js"></script>
<script src="/js/bootstrap/bootstrap3.3.7.min.js"></script>
<div class="center-block" style="width:150px;background-color:#ccc;">该 div 显示在中间</div>