Interactive Credit Card Form with Validation

This one took me forever. I had to learn how to do validation from scratch and work with regular expressions. The screen I was working from was barely showing my box and drop shadows, so now it looks a bit intense on normal screens, hahah.

Anyway, I learned a ton building this. I'm proud of myself for sticking with it! If anyone feels like looking into my code and finding more efficient ways of writing the validation functions or CSS, please let me know :)