Is it possible to put two different background pictures into the right and left sides of the following ikiwiki css?

https://raw.github.com/spiffin/ikiwiki_lessish/master/lessish.css

Is it also possible to have a background like this: http://ysharifi.wordpress.com/
or this tex.stackexchange.com

I am not a css expert so, it would be nice if you could provide some details.