I don't know much about cookie aside from the fact that I could use them as a save system for my web browser game.

Can I use theme of the game is embed on itch?

I would try, but I'm at work at the moment

Sure you can, but cookies aren't designed for it and nowadays it's better to use localStorage, which is made for the purpose.

Ah, I didn't know about this, I'll look into it, thanks =)