Each card and style has a number internally. That's the number it has when created.
The order placed is simply the order of appearance, numerically.
No, that's actually a lie. It's just picking the order based on the order in the webstorage container. Which should be equal to the order of creation, but may not be on all browsers.
I can give it an order I guess. I have also been pondering making a drag-and-reshuffle feature. I miss that functionality too :P