<!DOCTYPE html>
<html>
  <body>
    <div>
      <div style="float: left; padding-top: 20px">
        <a href="#" onclick="parent.postMessage({msg: 'DONE'}, '*'); return false;">test</a>
      </div>
    </div>
    <div style="position: absolute">
      A
    </div>
    B
  </body>
</html>