One of the key advantages of our Activity System with LSS over OpenGL is that you can easily theme your Activities with LSS. With OpenGL you'd have to rewrite the screen for every theme you want to support. With LSS, just like with CSS, you can just have an LSS StyleSheet for each theme. You can also create your own theme. All that is explained on this page.
Creating own themes doesn't work as of now. But we're working on it!
How Themes Work