I am a little unclear as to what the question is so I was wondering if there are any more details you can provide? Are you asking how we add different controls and layouts to the skin so that they can be styled?
Right now we don't have the ability to expose the option for customers to add their own configurable components to the skin (such as custom controls or Adobe XD prototypes to the skin) as that requires changes to both rule and platform engine code (which we don't expose). To work around this I recommend that you create a CSS file, which has the CSS you want for the custom component/control you are trying to style, you can then include that CSS file on your application skin.
Hope that helps, let me know if you have any more questions.