I believe it goes like this:
In your includes directory find and open your header.php file for the very last line at the bottom of your file add this:
<table width="100%" cellpadding="10" cellspacing="0" border="0">
<tr>
<td class="darktable">
<table width="100%" cellpadding="10" cellspacing="0" border="0">
<tr>
<td class="lighttable">
Then in your footer.php file for the very first line at the top of the file add this:
</td>
</tr>
</table>
</td>
</tr>
</table>
Then I believe you will get something simular to what you see here. I haven't used this anywhere but that's about how I think it's working.
Good Luck