Interactive Card Details Form using HTML, CSS and Javascript

I enjoy making this project. never expected to reach a 150 score here in Frontendmentor, this is a milestone for me as I am learning this coding for myself. hopefully, as I progress I can build more awesome websites in the future.

--difficulty on this project:

• putting error display on the input
• space after four number on the card number input

any tips are much appreciated for me to improve my design and my coding approach.