DIV嵌套显示有关问题 _ASP

DIV嵌套显示问题
<!DOCTYPE html>
<HTML>
<HEAD>
<TITLE>选择参培人员</TITLE><META HTTP-EQUIV="Pragma" CONTENT="no-cache">
<META HTTP-EQUIV="Content-Type" content="text/html; charset=gb2312">
<link rel="stylesheet" type="text/css" href="jquery-easyui/themes/default/easyui.css">
<link rel="stylesheet" type="text/css" href="jquery-easyui/themes/icon.css">
<link rel="stylesheet" type="text/css" href="jquery-easyui/demo.css">
<script type="text/javascript" src="jquery-easyui/jquery-1.8.0.min.js"></script>
<script type="text/javascript" src="jquery-easyui/jquery.easyui.min.js"></script>

<style type="text/css">
body{ border:0px; margin:0px; padding:0px; font-size:12px;}
  #main{ overflow:hidden;width:600px;margin:0 auto; }
   #left{float:left; width:300px;}
    #center{float:left; width:150px;}
#right{  overflow:hidden;width:150px;}
</style>

<SCRIPT LANGUAGE="JavaScript">

function change(){
  $('#main').dialog({
    title: '请选择参加培训人员',
    width: 650,
    height: 380,
    closed: false,
    cache: false,
    modal: true
});


}



</script>

</HEAD>
<BODY TEXT="000000" BGCOLOR="FFFFFF" >

<p align="center"><img src="jquery-easyui/themes/icons/right22.gif" class="pointer" onClick="change()"/><br/><br/></p>

<FORM METHOD=post ACTION='peixunjilu_add_s.asp' NAME='_wAddress'>
    <div id="main" style="visibility: hidden;">
         <div id="left"> <div class="easyui-layout" style="width:300px;height:300px;">
      <div data-options="region:'west',split:true" title="请选择部门" style="width:150px;"><ul id="tt" class="easyui-tree" data-options="url:'jquery-easyui/tree_data.asp',animate:true"></ul></div>
  <div data-options="region:'center',split:true" title="待选人员" style="width:150px;"><ul style="margin:0px; padding:0px; text-align:center"><select NAME="tmpleftList" id="leftList" multiple="multiple" style="width:141px;height: 265px;" ondblclick="changeValue();document.forms[0].tmprightListRef.value=selectToString(fieldAddress);" onKeyPress="if (window.event.keyCode==13){    AddClick(fieldAddress);    document.forms[0].tmprightListRef.value=selectToString(fieldAddress);}"></select></ul>
  </div>
</div>

        </div>
            <div id="center" >
            <ul style="padding-left:5px;padding-top:0px; margin:0px">