In the simplest terms, it renders native UI (the JSX part maps to UI components that the iOS and Android frameworks provide) but it maintains a bridge so that y

In the simplest terms, it renders native UI (the JSX part maps to UI components that the iOS and Android frameworks provide) but it maintains a bridge so that you can write your business logic in JS and have it work against those native components (as far as I understand it). It's not the same as using a web widget as your main interface and having it render the same kind of HTML and CSS you deploy on the web.