Payment

Credit card forms are so common that labels are almost completely unnecessary.

I use the logo and primary color of the credit card provider to indicate valid input.

I'm not sure about how to handle this particularly interesting invalid expiration date. Is the month invalid or the year invalid? Perhaps both should become invalid when either one of them is prior to the current date.

I chose to make only the year invalid on the assumption that you entered it after the month, and that typing in a field should only affect that field.