Interactive card details form using html , css and javascript

I disabled the submit button before form validation but don't know how to enable it after validation.Please how do I go about that?

I used event bubbling to easily collect form values but could not use it to ensure all fields validation before submission. What do I do?

Adding border to input focus state was hard so I use "outline" instead. I tried the same approach for adding linear-gradient to input active state but it never worked.