that's not gonna be ideal (nor will it work real well), since the css isn't a 1 for 1 as the message gets assembled by the mailer.inc.php class..
i'd suggest checking out the /templates/default/email_html.tpl file..
the philosophy is to be using tables for HTML email as well as inline css, since that's what most email clients will tolerate..
edit that file and you can stick in an additional tr, td, img kinda thingie to get your logo in
