Header icon color and background

I’ve changed the header color and need to update the header icons for better contrast. But I can’t take control of every element. This is how it looks:
Untitled
Looks like a circus, I know, the colors are just for troubleshooting.

I tried every suggestion from here as well as every apparently relevant class I could find when inspecting the html code.

But still when I hover over the icons, I get these black frames, and the icons turn grey.

How can I find out which classes I need to control to fix this?