When going through styling for the two frameworks, React uses traditional CSS, but React Native uses stylesheets. Stylesheets are extremely similar to CSS, but are put inside each component instead of in a separate linked CSS file. The tags for styling are largely similar, but some tags have small differences from each other.
React Native, very obviously, shares tons of similarities with React. I think one of the main questions is whether React Native is worth learning. If you want to learn a framework for mobile app development and you already know React, absolutely learn React Native, it’s only a couple steps away from being exactly the same. If you don’t know React and want to learn how to develop mobile apps, I’d start with learning React. It’ll be more useful to get the base framework under your belt, and you can always learn Native afterwards.