All game logic is contained in here. Game state is stored in a state object, with a reducer processing every command, which is sent to it as a plain string. Every move is processed deterministically, so it can be done simultaneously on both client and server.
This serves mostly as a bridge between Game logic and the Hathora server, and handles users joining the game, and throwing out invalid moves which the Game logic processes and returns an undefined state.
Built in plain React, a lot of the bridging to the server is handled in context/GameContext.tsx. The main game's view is in pages/Game.tsx, and is graphics are just a plain inline SVG.