Interactive card details form with Vanilla JS

By far my worst submition here, code is a total mess and filling the form in small screen sizes was simply awfull, but here I am... the validation part was a headache and it sure has tons of bugs, but I learned a bit more on key related events. Also there was something that I couldn't do, the inputs when on focus are supposed to have a border with linear gradient from top to bottom, if you know how to do it please let me know. I definitely want to try this challenge again from scratch, any feedback is appreciated, I need to recover XD