I have been looking, however, I have had little luck finding any way to style the React.js file that I have created, I converted it from a standard web page, so I have the o
Technically you can add the CSS in the HTML document as you would with a normal CSS file. So long as your React components have the same classes (except obviously applied as className no just class) then it will work.
If you're looking for something more modern and Javascript-oriented, you can look into CSS Modules, and read more about them here:
https://css-tricks.com/css-modules-part-1-need/
There's obviously a bit more of a learning curve with the second approach though.