.gradualChange{
width: 300px;
height: 300px;
border:20px solid;
//兼容
border-image: -webkit-linear-gradient(#000,#333,#000) 30 30;
border-image: -moz-linear-gradient(#000,#333,#000) 30 30;
border-image: linear-gradient(#000,#333,#000) 30 30;
}
css3实现border渐变色
原文地址：http://blog.51cto.com/10155134/2176604