Div半透明满屏遮盖和不透明显示

<div id="topDivBG" style="display: none; position: absolute; z-index: 1; background: url(../image/transparent.png);
width: 100%; height: 100px; top: 0; left: 0;" onclick="hiddenTopDiv();return false;">
<div id="topDivContent" style="font-size: 14px; text-align: center; font-weight: bold;
background-color: #ffffff; position: absolute; top: 223px;
left: 400px; width: 400px; height: 109px; border-width: 4px; border-color: #3078b0;
border-bottom-style: solid; border-right-style: solid; border-left-style: solid;
border-top-style: solid;" onclick="event.cancelBubble = true;">
<table border="0" width="100%" cellpadding="10" cellspacing="4">
<tr>
<td rowspan="7" style="width:40px;"></td>
<td align="right"><span style="cursor:hand;cursor:pointer;" onclick="hiddenTopDiv();return false;" title="close">X</span></td>
</tr>
<tr><td></td></tr>
<tr><td></td></tr>
<tr>
<td align="left"> Sorry, this item has been discontinued.</td>
</tr>
<tr>
<td align="left">Click <a href="search.aspx?cateid=<%=categoryId.ToString()%>">here</a> to search for similar products.</td>
</tr>
<tr><td></td></tr>
</table>
</div>
<input type="hidden" id="hidIsDelete" runat="server" />
</div>
<script language="javascript">
//获取滚动条高度
function getScrollTop() {
var scrollPos = 0;
if (typeof window.pageYOffset != 'undefined') {
scrollPos = window.pageYOffset;
}
else if (typeof window.document.compatMode != 'undefined' &&
window.document.compatMode != 'BackCompat') {
scrollPos = window.document.documentElement.scrollTop;
}
else if (typeof window.document.body != 'undefined') {
scrollPos = window.document.body.scrollTop;
}
return scrollPos;
}

function showTopDiv() {
if (document.getElementById("hidIsDelete") != null && document.getElementById("hidIsDelete").value == "1") {
var topDivBG = document.getElementById("topDivBG");
topDivBG.style.width = document.body.scrollWidth + "px";
topDivBG.style.height = document.body.scrollHeight + "px";

var topDivContent = document.getElementById("topDivContent");
var Conleft = document.body.offsetWidth / 2 - 200;
var Contop = document.documentElement.clientHeight / 2 + getScrollTop() - 80;
topDivContent.style.left = Conleft + "px";
topDivContent.style.top = Contop + "px";

//window.setTimeout(showTopDiv, 300);
}
}
function hiddenTopDiv() {
var topDivBG = document.getElementById("topDivBG");
topDivBG.style.display = "none";
}
function hiddenTopDiv() {
var topDivBG = document.getElementById("topDivBG");
topDivBG.style.display = "none";
}
</script>