#shangxia{position:fixed;top:45%;right:45%;display:block;margin-right:-540px; z-index:999;}
#shang,#comt,#xia{background:url(../images/huadong.png) no-repeat;position:relative;cursor:pointer;height:25px;width:29px;margin:10px 0 0;}
#comt{background-position:left -30px;height:32px;}
#xia{background-position:left -68px;}
#comt:hover{background-position:right -30px;}
#shang:hover{background-position:right 0;}
#xia:hover{background-position:right -68px ;}