Is there any open-source ui library for web app and mobile (native) apps?

I'm googling for a cross patform ui library, but I can't find one.

I don't care about native ui, as I need to customize almost everything for same ux.

I think I can achieve this using two template files (web/native).. Then use opengl for native, and use html for web.

Does this make sense? Any idea to apply css to mobile apps or convert mobile ui to web ui?