In your html code this code to onclick event or href
to close html banner
CLOSE BUTTON CODE
<a href="javascript:PushdownAd.get('PushdownAd1').close();"> CLICK TO CLOSE</a>
OR
<a onmouseover="javascript:PushdownAd.get('PushdownAd1').close();"> ROLLOVER TO CLOSE</a>
OR
<a onmouseout="javascript:PushdownAd.get('PushdownAd1').close();"> ROLLOFF TO CLOSE&/a>
If you are using option first html banner disapper when main banner opens then add toggle(0); to onlclick or href to close html banner
CLOSE BUTTON CODE
<a href="javascript:PushdownAd.get('PushdownAd1').close();toggle(0);"> CLICK TO CLOSE</a>
OR
<a onmouseover="javascript:PushdownAd.get('PushdownAd1').close();toggle(0);"> ROLLOVER TO CLOSE</a>
OR
<a onmouseout="javascript:PushdownAd.get('PushdownAd1').close();toggle(0);"> ROLLOFF TO CLOSE</a>