One minor improvement I would make is to prefetch the backgrounds for the specific card types (Visa, MC, Amex) so that the swapping appears seamless. This is a

One minor improvement I would make is to prefetch the backgrounds for the specific card types (Visa, MC, Amex) so that the swapping appears seamless. This is a great idea and I will totally keep it in mind for future projects. The "flip to the other side" to fill out the CVV is great. I might provide a second button/link, appearing once the CVV is completed, that says something to the effect of "valid input, next step"