<title>Bootstrap .clearfix 实例</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="//cdn.bootcss.com/bootstrap/3.3.6/css/bootstrap.min.css">
<script src="//cdn.bootcss.com/jquery/2.1.1/jquery.min.js"></script>
<script src="//cdn.bootcss.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
<div class="container-fluid">
<div class="col-xs-6 col-sm-3" style="background-color:lavender;">
重置窗口大小，查看效果。也尝试删除有 clearfix 的 div 查看效果。
<div class="col-xs-6 col-sm-3" style="background-color:lavenderblush;">列 2</div>
<div class="clearfix visible-xs"></div>
<div class="col-xs-6 col-sm-3" style="background-color:lightcyan;">列 3</div>
<div class="col-xs-6 col-sm-3" style="background-color:lightgray;">列 4</div>