I'm working on turning Photon's design into a UI library called Mono. You can see my progress here.
It's being made from scratch so that it's the highest quality UI library possible. It will also make it very simple to implement new features, and will make Photon's UI overall look better.
It's also technically usable currently, but you do have to do some setup for it to work that I haven't written in the docs yet.
This is really cool! I'm not the biggest fan of web development but this looks really clean and simple to use. The examples are also straightforward and easy to understand. It would be nice to document what does and doesn't work with JavaScript disabled though.