<style>
a{display:inline-block; width:100px; height:40px;
position:relative; overflow:hidden;}
input{position:absolute; right:0; top:0; font-size:100px;
opacity:0; filter:alpha(opacity=0);}
</style>
<a href="#">
<input type="file" />
</a>
原文：http://www.cnblogs.com/talentzemin/p/4190343.html