简单的遮罩层

<style>        #test {         width:100%;         height:100%;         background-color:#000;         position:absolute;         top:0;         left:0;         z-index:-2;         opacity:0.3;         /*兼容IE8及以下版本浏览器*/         filter: alpha(opacity=30);         display:none;     }     #log_window {         width:80%;         height:80%;         margin: auto;         position: absolute;         z-index:3;         top: 0;         bottom: 0;         left: 0;         right: 0;         display:none;     }

 </style>

 <button οnclick="show()">显示</button>     <div id="test"></div> <div id="log_window"> <a href="javascript:;" οnclick="cancel_shield()" id="clo">关闭</a> </div> <script>     function show(){         var s = document.getElementById("test");         s.style.display = "block";         var l = document.getElementById("log_window");         l.style.display = "block";     }      function cancel_shield(){         var s = document.getElementById("test");         s.style.display = "none";         var l = document.getElementById("log_window");         l.style.display = "none";     } </script>