Actually that's what the little colored bars above each card represent. The number of the bars that are filled in represent the card's level. In the video it is all max level cards so that's why all of the bars are filled. It's a clever way to show both the current card level (number of bars filled in), the max possible level (number of bars total), and the rarity (color of bars) all at once! Credit goes to @nateaguila for that design of course.