兼容IE7+、firefox、chorme
Document
*{margin:0;padding:0;}
body{margin:30px;}
.upload2{overflow:hidden;position:relative;width:134px;height:40px;cursor:pointer;background:url(icon_upload.png) no-repeat;}
.upload_file2{position:absolute;left:0;top:0;font-size:90px;margin:-20px 0 0 -1100px;opacity:0;filter:alpha(opacity=0);cursor:pointer;}