jQuery遮罩层效果（弹出层跟随滚动条移动）

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
    <title> New Document </title>
    <meta name="Generator" content="EditPlus">
    <meta name="Author" content="">
    <meta name="Keywords" content="">
    <meta name="Description" content="">
    <script src="http://code.jquery.com/jquery-1.10.1.min.js"></script>
    <script type="text/javascript">
//显示灰色 jQuery 遮罩层
function showBg() {
    var bh = $("body").height();
    var bw = $("body").width();
    $("#fullbg").css({
        height:bh,
        width:bw,
        display:"block"
    });
    $("#dialog").show();
}
//关闭灰色 jQuery 遮罩
function closeBg() {
    $("#fullbg,#dialog").hide();
}
</script>
<!–[if lte IE 6]>–>
<script type="text/javascript">
// 浮动对话框
$(document).ready(function() {
    var domThis = $('#dialog')[0];
    var wh = $(window).height() / 2;
    $("body").css({
        "background-image": "url(about:blank)",
        "background-attachment": "fixed"
    });
//domThis.style.setExpression('top', 'eval((document.documentElement).scrollTop + ' + wh + ') + "px"');
});
</script>
<style type="text/css">
body {
    font-family:Arial, Helvetica, sans-serif;
    font-size:12px;
    margin:0;
}
#main {
    height:1800px;
    padding-top:90px;
    text-align:center;
}
#fullbg {
    background-color:Gray;
    left:0px;
    opacity:0.5;
    position:absolute;
    top:0px;
    z-index:3;
    filter:alpha(opacity=50); /* IE6 */
    -moz-opacity:0.5; /* Mozilla */
    -khtml-opacity:0.5; /* Safari */
}
#dialog {
    background-color:#FFF;
    border:1px solid #888;
    display:none;
    height:200px;
    left:50%;
    margin:-100px 0 0 -100px;
    padding:12px;
    position:fixed !important; /* 浮动对话框 */
    position:absolute;
    top:50%;
    width:200px;
    z-index:5;
}
#dialog p {
    margin:0 0 12px;
}
#dialog p.close {
    text-align:right;
}
</style>
<body>
</head>
<div id="main"> <a href="#" onclick="showBg();">点击这里看 jQuery 遮罩层效果.</a> </div>
<!– jQuery 遮罩层 –>
<div id="fullbg"></div>
<!– end jQuery 遮罩层 –>
<!– 对话框 –>
<div id="dialog">
    <p><a href="#" onclick="closeBg();">关闭</a></p>
    <p>正在加载，请稍后…</p>
</div>
</body>
</html>
jQuery遮罩层效果（弹出层 跟随滚动条移动）

jQuery遮罩层效果（弹出层跟随滚动条移动）
