处于页面中间的alert

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title>
<style type="text/css">
<!--
#Layer1 {
    position:absolute;
    width:200px;
    height:115px;
    z-index:1;
}
-->
</style>
</head>

<body>
 <DIV id=L1  style="HEIGHT: 107px; LEFT: 341px; POSITION: absolute; TOP: 585px; WIDTH: 205px; Z-INDEX: 1">
  <TABLE bgColor=#ffffff border=1 borderColorDark=#ffffff borderColorLight=#000000 cellPadding=0 cellSpacing=0 width="100%">
                    <TR>
                      <TD height=1 width=178>□::阿里西西::</TD>
                      <TD align=middle onclick="L1.style.visibility='hidden'" 
                      style="CURSOR: hand" width=21>х</TD></TR>
                    <TR vAlign=top>
                      <TD colSpan=2 
                        height=91>欢迎光临本站!<BR><BR>本站域名:<BR>http://www.k688.com 
                      </TD></TR></TABLE></DIV>
<SCRIPT LANGUAGE="JavaScript">
function moveit() //这个函数用于把层放到浏览器中间
{
L1.style.left=((document.body.offsetWidth-parseFloat (L1.style.width))/2)+document.body.scrollLeft;
L1.style.top=((document.body.offsetHeight-parseFloat (L1.style.height))/2)+document.body.scrollTop;
}
window.onload=moveit; //网面打开时时执行moveit()
window.onresize=moveit; //当调整浏览器大小时执行moveit()
window.onscroll=moveit; //当拉动滚动条时执行moveit()
</SCRIPT>

<a href="http://www.alixixi.com/Dev/HTML/jsrun/">欢迎访问阿里西西网页特效集</a>
<table width="280" border="1" cellspacing="0" cellpadding="0">
  <tr>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
  </tr>
  <tr>
    <td><div id="Layer1">是多少身份是东方士大夫</div></td>
    <td>&nbsp;</td>
  </tr>
</table>

<script type="text/javascript" language="javascript">
                
            function sAlert(txt){
    var eSrc=(document.all)?window.event.srcElement:arguments[1];
    var shield = document.createElement("DIV");
    shield.id = "shield";
    shield.style.position = "absolute";
    shield.style.left = "0px";
    shield.style.top = "0px";
    shield.style.width = "100%";
    shield.style.height = document.body.scrollHeight+"px";
    shield.style.background = "#333";
    shield.style.textAlign = "center";
    shield.style.zIndex = "10000";
    shield.style.filter = "alpha(opacity=0)";
    shield.style.opacity = 0;
    var alertFram = document.createElement("DIV");
    alertFram.id="alertFram";
    alertFram.style.position = "absolute";
    alertFram.style.left = "50%";
    alertFram.style.top = "50%";
    alertFram.style.marginLeft = "-225px" ;
    alertFram.style.marginTop = -75+document.documentElement.scrollTop+"px";
    alertFram.style.width = "450px";
    alertFram.style.height = "150px";
    alertFram.style.background = "#ccc";
    alertFram.style.textAlign = "center";
    alertFram.style.lineHeight = "150px";
    alertFram.style.zIndex = "10001";

    strHtml  = "<ul style="list-style:none;margin:0px;padding:0px;width:100%"> ";
    strHtml += "    <li style="background:#DD828D;text-align:left;padding-left:20px;font-size:14px;font-weight:bold;height:25px;line-height:25px;border:1px solid #F9CADE;">[系统提示]</li> ";
    strHtml += "    <li style="background:#fff;text-align:center;font-size:12px;height:120px;line-height:120px;border-left:1px solid #F9CADE;border-right:1px solid #F9CADE;">"+txt+"</li> ";
    strHtml += "    <li style="background:#FDEEF4;text-align:center;font-weight:bold;height:25px;line-height:25px; border:1px solid #F9CADE;"><input type="button" value="确 定" id="do_OK" onclick="doOk()" /></li> ";
    strHtml += "</ul> ";
    alertFram.innerHTML = strHtml;
    document.body.appendChild(alertFram);
    document.body.appendChild(shield);
    this.setOpacity = function(obj,opacity){
        if(opacity>=1)opacity=opacity/100;
        try{ obj.style.opacity=opacity; }catch(e){}
        try{ 
            if(obj.filters.length>0 && obj.filters("alpha")){
                obj.filters("alpha").opacity=opacity*100;
            }else{
                obj.style.filter="alpha(opacity=""+(opacity*100)+"")";
            }
        }catch(e){}
    }
    var c = 0;
    this.doAlpha = function(){
        if (++c > 20){clearInterval(ad);return 0;}
        setOpacity(shield,c);
    }
    var ad = setInterval("doAlpha()",1);
    this.doOk = function(){
        //alertFram.style.display = "none";
        //shield.style.display = "none";
        document.body.removeChild(alertFram);
        document.body.removeChild(shield);
        eSrc.focus();
        document.body.onselectstart = function(){return true;}
        document.body.oncontextmenu = function(){return true;}
    }
    document.getElementById("do_OK").focus();
    eSrc.blur();
    document.body.onselectstart = function(){return false;}
    document.body.oncontextmenu = function(){return false;}
}
        </script>
        <input type="button" value="点击这里" onclick="sAlert('我是一个渐变的sAlert',this);" />
</body>
</html>