GWT will not ensure it 'looks' the same on all OS+Browser combinations. It only guarantees to abstract all the compatibility headache away from the developer.
I will also cross post this to the HTML/CSS forums. That way you can get better advise.
Isaac Ferguson wrote:Ok then what you mean is that with GWT I can make it work the same in any browser bot for the looks I should use CSS and all that stuff?
GWT shields you from worrying too much about cross-browser incompatibilities. If you stick to built-in widgets and composites, your applications will work similarly on the most recent versions of Internet Explorer, Firefox, Chrome, and Safari. (Opera, too, most of the time.)