Did you also change the inline css that you have on the original div?
Currently it reads:
but you'll need to remove the positioning from it, since you're already declaring an absolute position in your head CSS. Unfortunately, your inline CSS will override it. SO, best thing is remove all CSS inline, so you only have:
<div id='mypopup' name='mypopup' style='position: relative; width: 179px; height: 36px; display: none;'>
Then for your head css:
<div id="mypopup" name="mypopup">
Let us know if this works for you.