Nice work, this is fun! I've only played against the AI so far, managed to win on Beginner.

I think it would benefit from some little animations so it's clearer what's going on. But making that work nicely across both desktop and mobile could be a real pain, so I wouldn't blame you for punting it until later. :)

A smaller suggestion: maybe draw all the spare pieces on screen, rather than just displaying e.g. "15 pcs" as text. That way you can see at a glance when your stock is dwindling. Experts won't need that but it could be useful for beginners.