.close_frame{display:inline-block;height:14px;width:14px;background:url("../images/closeiframe.png") no-repeat 0 0; transition:transform 0.2s ease-in-out;}
.close_frame:hover{background-position:0 -15px; transform:rotate(180deg);}
原文：http://www.cnblogs.com/zhangwenkan/p/5104937.html