Hello and welcome to the forum 🙂
We are aware that we do not rank highly in regards to looks / style. While we have made many improvements in this area already, we will continue to work on this.
In regards to styling via CSS: All our frontend elements have proper classes and can be addressed via CSS. REI3 Professional customers can already supply their own custom CSS content via the customizing features.
As an open source software, you can of course adjust any CSS you like without the need for any licenses, if you are willing to work on the source.