If you expand the browser width after the puzzle activity is open, the image scales up but the cards do not. This leave small cards covering only a portion of the image.
I changed the card dimensions (width/height) to percentages and then changed the positioning (top/left) to percentages so everything should scale up/down.
If you expand the browser width after the puzzle activity is open, the image scales up but the cards do not. This leave small cards covering only a portion of the image.