You can recreate almost anything in css/html but you'd have to write a different style for each OS yourself, and it will never match the actual "feel" of the UI

You can recreate almost anything in css/html but you'd have to write a different style for each OS yourself, and it will never match the actual "feel" of the UI. It'll be a little off. Also, for example Mac OS X has lots of little widgets like the share button. Maybe someone could make a Bootstrap-like project for these kinds of things?