This project took a long time, following along with Kevin Powel, then adapting the things he did to work with react.js and a component centric way of building. It took me a couple of false starts until I worked out a way to adapt what he was doing.
I learned a huge amount from this project, a lot more than I thought I would! I highly recommend it to anyone thinking of doing it.
Kevin explains everything very well, but there was one thing I didn't understand. When developing his font size system, he calls the font sizes --fs-900, --fs-800, --fs-700 etc. down to --fs-400. I have no idea where he got these names/numbers from?? There was nothing in the Figma design file like this, and I couldn't find anything on google about it.