关于CSS设置背景透明的问题

不是复杂的边框的话可以在 border 或 box-shadow 上用 rgba

<div id="container">
<div id="content" />
<div id="background" />
</div>

<style>
#container { position: relative; width: 100px; height: 100px; }
#background { position: absolute; top:0; left: 0; background: green; }
#content { margin: 10px; width: 90px; height:90px; background: red; }
</style>

never mind, check this out: http://jsbin.com/oloqe5/edit