I like this patch! It looks good, blends in well with the rest of my desktop, and it uses the default colors for text and background, which makes it work with dark color themes, too. Would be nice to have this in default Code::Blocks some day, either replacing the default tab style, or (maybe even be better) as an additional selectable style.
Maybe a configure option could be created, so people who don't want the GTK depencendy can disable it.