1. Create a new theme layer. (Follow the steps
in this post to create a theme layer.) If you have already created a theme layer for the style, just add the following code to it.
2. Copy and alter the following code and modify the part in red as you see fit. Paste it right after the layerinfo stuff.
function Page::print_custom_head()
{
"""
""";
}
Just alter the values in red. I suggest you leave everything else as is, unless you know what you're doing.
Tips and tricks:
If you want the outer box to be the same width as your banner, that's possible too. Go to the customisation wizard and look at the very bottom of the "Presentation" tab. Enter the width of the journal in pixels -- it should be (your banner width - 32) pixels. For example, if your banner is 800px wide, the width of the journal should be set to 768px. Don't forget to change Unit of journal width to pixels.
Why 32, you ask? It's because of the padding (and border) around the sidebar and main content. It's a little off in IE, as far as I can tell, so just play around with it until it looks right, okay?