.button_top{display:none;width:52px;height:52px;background-image:url(images/top.png);background-position:center;background-repeat:no-repeat;width:52px;height:52px;background-image:url(images/top.png);background-position:center;background-repeat:no-repeat;position:fixed;bottom:20px;right:20px;cursor:pointer;z-index:999}