Drop shadow on fluid theme?

Hi,

I’m playing with Zenlike (http://themes.wordpress.net/columns/2-columns/1115/zenlike-10/) which though its described as fixed width is actually fluid. My question is now that I’ve removed the wood background and replaced with a nice grey. How easy is it to add a drop shadow? And can this be done on a fluid page? I’ve done it on a non-wordpress site before using CSS – but that time I knew the exact width of the content so placing a shadow down the sides wasn’t difficult….

Your thoughts?

Thanks