css3 box-sizing属性使用参考指南

.box_sizing{
width:180px;
padding:40px 20px;
background:#a0b3d6;
overflow:hidden;
}
.box_sizing .in{
width:100%;
border:12px double #34538b;
background:white;
padding:5px;
box-sizing:border-box;
-o-box-sizing:border-box;
-ms-box-sizing:border-box;
-moz-box-sizing:border-box;
-webkit-box-sizing:border-box;
}

<div class="box_sizing">
<div class="in">此处12像素的border和5像素的padding值算在宽度里面了~~</div>
</div>