Change height footer on mobile

Hello, I have found already a way with CSS to change the height of the header on mobile screens. But now I want to change the footer also, only on mobile. There must be as little space above and beneath the text.
It is a wp/divi site: I have an idea but not the correct skills in CSS to fix this.
help will be much appreciated,

Hello Conny,

This forum is for Sydney theme support. Please contact your theme support regarding this issue.

Kind Regards, Roman.

Sorry, my mistake.