Newsletter sign up with success message with HTML CSS JS

What are you most proud of, and what would you do differently next time?

I will try to get my head around mobile approach first.

What challenges did you encounter, and how did you overcome them?

My first approach was to create a second HTML file for success page. Later i have decided to use single HTML file and that was challenging at first. Then i have used JS to adjust different attributes.

What specific areas of your project would you like help with?

Error states on e-mail inputs does not work properly. I am open to any feedback.