引导网格结构
Bootstrap中的网格结构如下所示：
示例
<div class = "box">
<div class = "row">
<div class = "col-*-*"></div>
<div class = "col-*-*"></div>
<div class = "col-*-*"></div>
<div class = "col-*-*"></div>
</div>
<div class = "row">...</div>
</div>
<div class = "box">
....
</div>