蒙板是两个div，其中popWindow样式的div用于遮住整个页面，并半透明。maskLayer 在popWindow上面，用于显示蒙板的信息，比如“载入中……“
<html>
<head>
<style type="text/css">
.popWindow {
background-color:#9D9D9D;
width: 100%;
height: 100%;
left: 0;
top: 0;
filter: alpha(opacity=50);
opacity: 0.5;
z-index: 1;
position: absolute;
}
.maskLayer {
background-color:#000;
width: 200px;
height: 30px;
line-height: 30px;
left: 50%;
top: 50%;
color:#fff;
z-index: 2;
position: absolute;
text-align:center;
}
</style>
<script language="javascript" type="text/javascript">
function showDiv() {
document.getElementById('popWindow').style.display = 'block';
document.getElementById('maskLayer').style.display = 'block';
}
function closeDiv() {
document.getElementById('popWindow').style.display = 'none';
document.getElementById('maskLayer').style.display = 'none';
}
</script>
</head>
<body>
<div onclick="showDiv()" style="display:block; cursor:pointer">
弹出蒙板
</div>
<div id="popWindow" class="popWindow" style="display: none;">
</div>
<div id="maskLayer" class="maskLayer" style="display: none;">
<a href="#" onclick="closeDiv()" style="cursor:pointer;text-decoration: none;">
关闭蒙板
</a>
</div>
</body>
</html>