<div class="tooltiptop">
 <div class="bg"></div>
 <div class="main"><i>Jq顶部弹出框</i><span onClick="ToolTipTop.Hide();" title="关闭">X</span></div>
</div>

body {
 margin: 0;
 padding: 0;
}
.tooltiptop {
 width: 100%;
 height: 50px;
 margin-top:-50px;
 display:none;
}
.tooltiptop .bg {
 width: 100%;
 background-color: #333;
 height: 50px;
 opacity: .7;
 position: absolute;
 margin: 0;
}
.tooltiptop .main {
 width: 100%;
 position: absolute;
 margin: 0;
 height: 50px;
 line-height: 50px;
 text-align: center;
 color: #fff;
}
.tooltiptop .main span {
 float: right;
 color: #fff;
 margin-right: 20px;
 cursor: pointer;
}

var ToolTipTop={
 Show:function(Msg){
  $(".tooltiptop .main i").html(Msg);
  $(".tooltiptop").css("display","block").animate({marginTop:"0px"},500);
 },
 Hide:function(){
  $(".tooltiptop").animate({marginTop:"-50px"},500,function(){$(this).css("display","none")});
 }
}

<style type="text/css">
*{margin:0;padding:0;list-style-type:none;}
a,img{border:0;}
.demo{margin:0 auto 0 auto;padding:200px 0 0 0;width:400px;text-align:center;font-size:18px;}
.demo .action{color:#3366cc;text-decoration:none;font-family:"微软雅黑","宋体";}

#Header{
 position:fixed;z-index:9999999;top:0;right:0;left:0;height:38px;border-bottom:1px solid #e0dede;width:100%;
 background-color:#F7F7F7;
 background-image:linear-gradient(#fff, #f7f6f5);
 background-image:-moz-linear-gradient(#fff, #f7f6f5);
 background-image:-o-linear-gradient(#fff, #f7f6f5);
 background-image:-webkit-linear-gradient(#fff, #f7f6f5);
 
 box-shadow:inset 0 1px #fff, 0 1px 3px rgba(34,25,25,0.4);
 -moz-box-shadow:inset 0 1px #fff, 0 1px 2px rgba(34,25,25,0.4);
 -webkit-box-shadow:inset 0 1px #fff, 0 1px 3px rgba(34,25,25,0.4);
}
*html,*html body{background-image:url(about:blank);background-attachment:fixed;}
*html #Header{position:absolute;top:expression(eval(document.documentElement.scrollTop));}

.overlay{position:fixed;top:0;right:0;bottom:0;left:0;z-index:998;width:100%;height:100%;background:#f6f4f5;display:none;}
*html,*html body{background-image:url(about:blank);background-attachment:fixed;}
*html .destroy,*html .overlay{position:absolute;top:expression(eval(document.documentElement.scrollTop));}

.destroy{position:fixed;top:0px;left:50%;margin-left:-425px;*margin-left:-718px;_margin-left:-425px;margin-top:-292px;z-index:99996;opacity:0;filter:alpha(opacity=0);}
.sheet{position:relative;width:840px;height:290px;margin:auto;padding:0;background:#fff9e2 url("images/tips_bg.gif");
 box-shadow:inset 0 -1px 0 #FFF,0 1px 6px rgba(0,0,0,.3);
 -moz-box-shadow:inset 0 -1px 0 #FFF,0 1px 6px rgba(0,0,0,.3);
 -webkit-box-shadow:inset 0 -1px 0 #FFF,0 1px 6px rgba(0,0,0,.3);
 
 border-bottom:2px solid #efebda;
 border-bottom-left-radius:5px;
 border-bottom-right-radius:5px;
 -moz-border-bottom-left-radius:5px;
 -moz-border-bottom-right-radius:5px;
 -webkit-border-bottom-left-radius:5px;
 -webkit-border-bottom-right-radius:5px;
}
.sheet a.close{display:block;position:absolute;width:20px;height:20px;right:5px;top:5px;background:url("images/sheet_close.gif") no-repeat;}
.sheet a:hover.close{background-position:0 -30px;}
.sheet a:active.close{background-position:0 -60px;}
.sheet .head{padding:20px 15px;border-bottom:1px solid #f6f4ee;}
.sheet .head h2{padding:0;font-size:18px;font-weight:400;color:#444;text-align:center;}
.sheet .body{padding:10px 15px;border-top:1px solid #fff;}
</style>

<script type="text/javascript" src="js/jquery-1.4.2.min.js"></script>
<script type="text/javascript">
$(document).ready(function(){
 
 var h = $(document).height();
 $(".overlay").css({"height": h }); 
 
 $(".action").click(function(){
 
 $(".overlay").css({'display':'block'}).animate({'opacity':'0.8'});
 
 $(".destroy").stop(true).animate({'margin-top':'40px','opacity':'1'},400);
 
 });
 
 $(".close").click(function(){
 
 $(".destroy").stop(true).animate({'margin-top':'-292px','opacity':'0'},800);

 $(".overlay").css({'display':'none'}).animate({'opacity':'0'});
 
 });
 
});
</script>

<div id="Header"></div>

<div class="demo"><a class="action" href="javascript:void(0);">jquery float浮动层弹出层页面加载特效</a></div>

<div class="overlay"></div>

<div class="destroy">
 <div class="sheet">
 <div class="head">
 <h2>jquery顶部动画弹出层</h2>
 </div>
 <div class="body"></div>
 <a class="close" title="关闭" href="#"></a>
 </div>
</div><!--sheet end-->