GeneratePress - Styling, web design/dev. (entry level)

I have a website that is built with the Wordpress theme, GeneratePress. Unfortunately, I have used Elementor, instead of the Theme-specific elements. I need help to set up some quite basic CSS codes a I have a website that is built with the Wordpress theme, GeneratePress. Unfortunately, I have used Elementor, instead of the Theme-specific elements. I need help to set up some quite basic CSS codes and making a some simple templates with GeneratePress, that includes:GP elementsGP HeadersHooksCSS-codes