#demo{position: relative;} #demo:after{content:‘‘;border:1px solid #999;height:200%;width:200%;-webkit-transform: scale(0.5);transform:0.5;transform-origin: 0 0;-webkit-transform: 0 0;position: absolute;top:0;left:0;}
<div class="demo">我有0.5px的border</div>
原文：http://www.cnblogs.com/litterfour/p/7028836.html