This seems like a really fun game but unfortunately I can't figure out how to play it. I think you should consider adding a tutorial.
I also almost got stuck on the start of the game. The misunderstanding comes from using the same icon for dragging the card during initial deck creation, and "starting game". It's not clear you need to drag the cards to the bottom of the screen, and I instead tried double clicking or clicking and then clicking the arrow. Consider using a different type of element, or an arrow that moves between a selected card and the bottom of the screen.