div 图像 定位到 网页中间位置 不随滚动条滚动

<div id="img" style="position:fixed;left:10px;top:330px;z-index:11;" >

<img style="cursor:pointer" src="/templets/ydnk/images/zongjie.jpg" width=111px height=111px>

</div>

<div id="img0777" style="position:fixed;left:10px;top:640px;" >

<img style="cursor:pointer;" src="/templets/ydnk/images/zongjie.jpg" width=111px height=111px>

</div>

 

 

 

<script>
function hide1(){

//alert(document.documentElement.clientwWidth / 2+ ' ' +document.documentElement.clientHeight/2 );

document.getElementById("img").style.left=document.documentElement.clientWidth / 2+'px';

document.getElementById("img").style.top=document.documentElement.clientHeight / 2 +'px';
}
setInterval(hide1,"300");
</script>