Memory Game - React

This was another tough but good one! I'd especially welcome feedback on how I can better structure my app, and really get into the "thinking in React" state of mind. I feel like I'm getting there but not yet arrived.

There are a couple of issues on mobile (for very small screens) and honestly, I don't really want to think about a11y for this one as just dealing with React is enough, but I'm pretty sure a lot more work would be needed to make this production ready!

Any feedback/comments/criticisms most welcome!