div 绝对定位 居中 absolute fixed

html代码
<div class="pop_div">
      <div class="pop_div_inner">
          <div><img usemap="#MapBottom" src="/templets/ks120/images/bottom_pop_div/bg.gif"><map id="MapBottom" name="MapBottom"><area href="/a/nankeyiyuan/xinggongnenzhangai/tesejishu/2012/0107/904.html" coords="99,20,344,50" shape="rect"><area href="javascript:void(0);" onclick="openZoosUrl('chatwin');" coords="622,16,755,51" shape="rect"><area href="javascript:void(0);" onclick="openZoosUrl('chatwin');" coords="402,24,603,45" shape="rect"></map></div>
          
          
          
     </div>      
  </div>

css代码