ul.thumb {float: left;list-style: none;margin: 0; padding: 0px;width: 600px;background-color: 333333;}
ul.thumb li {margin: 0; padding: 5px;float: left;position: relative;width: 273px;height: 181px;}
ul.thumb li img {width: 273px; height: 181px;border: 0px solid #ddd;padding: 5px;background: #;position: absolute;left: 0; top: 0;-ms-interpolation-mode: bicubic; }
ul.thumb li img.hover {margin-top:15px;background:url(thumb_bg.png) no-repeat center center;border: none;}