Sign Up Page(Form Validation) - HTML, CSS, JavaScript

This is my fifth challenge following the article 16 Front End Project with designs to help with your coding skills. I quite enjoy the journey!

I find that regex is quite simple to understand, but is the online regex examples are too vigorous that make me fear of it at first hand. But with this challenge, I am able to first encounter regex, understand what is used for.

Any comments on my design is truly welcome.