The easiest way to produce rounded corners within jGrowl would be to use one of the existing rounded corners plugins and then to apply their methods to jGrowl notifications in one of the callbacks provided. There are many different ways of dealing with rounded plugins and each developer has a different preferred way of dealing with them. The bundle includes those options native to the browser as a demonstration, but rather than impose or require a library or duplicate my personal favorite I've opted to leave that code out and let people leverage other plugins. If you would like specific examples feel free to e-mail me and I'll provide you with them.