3
First of all, insert a new line near the top in your css file for the theme:
table#t1{
background-color: #FFFFFF;
width: 765px;
}
You can change the background color to whatever you want.
Then, in your theme.html for your theme, just under the <body> tag:
<table border="0" align="center" cellpadding="0" cellspacing="0" id="t1">
Don't forget to put the closing </table> tag just before the </body> tag at the bottom.