在html正文上面有一个广告，让整个文本向下滑动，让广告显示，然后再让广告滑到上面
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>广告条滚动</title>
<style type="text/css">
*{
padding: 0px;
margin: 0 auto;
}
#ad{
1000px;
height:300px;
font-size: 50px;
background: red;
margin-top:-300px;
}
#box{
1000px;
height:800px;
background: green;
}
</style>
<script type="text/javascript" src="./js/jquery-1.7.1.min.js"></script>
<script type="text/javascript">
$(function(){
$('#ad').animate({'marginTop':'0px'},3000,function(){//3秒ad显示
setTimeout(function(){//回调函数，定时器
$('#ad').animate({'marginTop':'-300px'},3000);//3秒ad消失
},3000);
});
})
</script>
</head>
<body>
<div id="ad">欢迎来到本网站</div>
<div id="box"></div>
</body>
</html>