Edit the css for the toggled responsive menu

Hi there.
I’m not a programmer, just a designer with some html/css skills.
I’m trying to edit the way the toggled menu looks, specially because the way I have it now it not only looks horrible (and unreadable) on a mobile device, but it also doesn’t work.
So I want to remove most of the stuff I added for the desktop menu, and have a plain and simple version of the menu when toggled.
But every time I try to do something, it applies it to the un-toggled version as well.

Any suggestions where I can edit this and have a separate result for the toggled menu?

My personal website, the one I’m trying to do this on: https://sketchtoon.com/

Thanks!