There are a variety of advanced React techniques that are good to be aware of. By testing and typing your code well, you can make it more robust against change. It will be easier to develop if you have the right scaffolding in place supporting your application.
Styling React is a complicated topic itself. There are multiple ways to achieve that and there's no clear consensus on what is the correct way in the context of React. I will provide you a good idea of the current situation.
As there's no one right way to structure React projects, I'll also provide some idea on how to do that. It's better to be pragmatic and figure out a structure that's the right one for you.