Wraping a PHPBB3 forum post content around Google Adsense Ad

Question

I am injecting this code ` in viewtopic_body.html just before

    <div class="content">{postrow.MESSAGE}</div>

However, the post content wraps on the right side of the Google Ad but not below the Ad. I have tried many variations of float but the bottom part of the Ad is always blank.

I want to know how this wrapping issue can be fixed WITHOUT touching any other file in the PHPBB3 forum software except viewtopic_body.html. (PHBB3 Ver. 3.0.7-PL1)