Child theme not overriding parent

Hi! I’m really a newbie on WordPress and I’m setting up a site for a local clinic. I use the Interface theme, and because I want to customize it a bit (fonts, colours, sidebar next to header) I created a child theme.

Unfortunately the child theme isn’t overriding the parent theme.

I’m not too familiar with functions and this is a responsive theme, so I might be missing something there?

Any thoughts would be of great help.

(P.S. I have created child themes before and never had issues before this.)