网页内容块悬浮

$(function() {
var adsHeight = $(".ads").height();//获取顶部的高度
$(window).scroll(function() {
var scrollTop = $(document).scrollTop();//滚动的高度
if(scrollTop >= adsHeight) { //如果滚动的高度大于等于顶部的高度，则让内容块悬浮
$(".pingmians ").css({
"position": "fixed",
"top": "0",
"max-width": "1240px",
"background": "#fff",
"z-index": "99"
});

} else {
$(".pingmians ").css({
"position": "static"
});

}
})

})