<div style="width:10px; height:10px; overflow:hidden;">
  <div style="opacity:0.5;">
    <div style="position:absolute; z-index:0; width:100px; height:100px; border:1px dashed black; ">
      <div style="position:relative; top:50px; left:50px; width:50px; height:50px; background:red;"></div>
    </div>
  </div>
</div>