animate循环动画---兼容ie8

.fd-guang{
     326px;
    height: 23px;
    background: url("../images/guang_07.png") no-repeat left top;
    position: absolute;
    left:0;
    top: 0;
}

var css = {top:'210px'};
$('.fd-guang').animate(css,3000,rowBack);
function rowBack(){
    if(css.top==='0px'){
        css.top='210px';
    }else if(css.top==='210px'){
        css.top='0px';
    }
    $('.fd-guang').animate(css,3000,rowBack);
}