简单遮罩层

<style>
    #test {
        width: 100%;
        height: 310px;
        background-color:#000; /*#F5F5F5;*/
        position: absolute;
        top: 165px;
        left: 0;
        z-index: 9999;/*最上层*/
        opacity: 0.0;/*透明度*/
        /*兼容IE8及以下版本浏览器*/
        filter: alpha(opacity=0);
        display: none;
    }
</style>
<script>
    //打开遮罩层
    function shield() {
        var s = document.getElementById("test");
        s.style.display = "block";
    }
    //关闭遮罩层
    function cancel_shield() {
        var s = document.getElementById("test");
        s.style.display = "none";
    }
</script>

<div id="test"></div>