This is an idea that has been floated by a few users, which means there is probably a need for it. As is usually the case, I don’t like to make wholesale changes to the codebase that effects users in a way that requires them to make a change to accommodate an update. So I wouldn’t want to change the plugin to put in different classes, since users with a custom stylesheet would need to be paying attention when they update to accommodate the new classes in their stylesheet. But this is something that we can certainly do on the fly using the wpmem_msg_dialog filter. This article will show you how to do just that.