Hey nice work! The core gameplay is fun, it's really satisfying to find cards that synergize, and it motivates me to get in fights to see what enemies might carry. The ability variety is also pretty nice. It might not have been an intentional feature, but if you just dip below 0 health you can bounce back with well timed cards, makes a nice cinch mechanic.
Any sort of menu to check or discard cards to manage your deck would probably be the nicest addition I can think of. This is a minor thing but, the book at the beginning seems like it would be an intractable object, but offers no text. If it's a stand in for the included text journal I would consider including a hint to check your files for it in game, or maybe even being a touch more specific about it in the itch.io page.
Overall quite the feat for 4 days, you should be proud!