Hi Jane and welcome, there are 24 packs per box (the box looks quite big because there's a slab of polystyrene at the bottom of the box), each pack contains 6 basic (green) character cards, there are 72 cards in this green set - you would usually get a full set in a box).
One pack in every 4 contains an orange subset (which is 20 cards in all, the evolution A set) and one in every 6 packs contains a stained glass card (pretty cool, not glass but nicely made from plastic... much nicer than previous cards in this style by other manufacturers). Lastly - and I think the odds are one every 12 packs - you get a blue foil card (12 cards in all - the Evolution B set).
Most boxes contain either one or two sketch cards too, which are rather fun...
Any more questions just ask away
