对div的控制

用javascript 对div进行显示和隐藏！
如何使div定位在网页中央？（要动态的）高人速度来只要能实现我就速度结贴！！！~~~~~

解决方案 »

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我记得以前见过类似win关机效果的div…………可惜现在找不到了……div上面有text和button 能提交表单或者能获得数据都行……高人啊
if (document.getElementById("ddd").style.display=="block"){
                document.getElementById("ddd").style.display="none";
            } else {
                document.getElementById("ddd").style.display="block";
            }
<html>
<head>
    <script>
  function   locking(){
  document.all.ly.style.display="block";
  document.all.ly.style.width=document.body.clientWidth;
  document.all.ly.style.height=document.body.clientHeight;
  document.all.Layer2.style.display='block';
  }
  function   Lock_CheckForm(theForm){
  document.all.ly.style.display='none';document.all.Layer2.style.display='none';
  return   false;
  }
    </script></head>
<body>
    <img src="http://powereasy.net/skin/since07/images/sf_cms_banner1.jpg">
    <p align="center">
        <input type="button" value="系统锁定" onclick="locking()">
    </p>
    <div id="ly" style="position: absolute; top: 0px; filter: alpha(opacity=60); background-color: #777;
        z-index: 2; left: 0px; display: none;">
    </div>
    
    <div id="Layer2" align="center" style="position: absolute; z-index: 3; left: expression((document.body.offsetWidth-540)/2); top: expression((document.body.offsetHeight-170)/2);
        background-color: #fff; display: none;" >
        <table width="540" border="0" cellpadding="0" cellspacing="0" style="border: 0   solid   #e7e3e7;
            border-collapse: collapse">
            <tr>
                <td style="background-color: #73A2d6; color: #fff; padding-left: 4px; padding-top: 2px;
                    font-weight: bold; font-size: 14px;" height="27" valign="middle">
                    [ 警 告 ]
                </td>
            </tr>
            <tr>
                <td height="130" align="center">
                    <input type="button" value=" 确定 " onclick="Lock_CheckForm(this);">
                </td>
            </tr>
        </table>
    </div>
    
</body>
</html>