Bounty Edit: This post explains better the problem
I've already made some posts asking how to adjust some little features from the themes you install in Gnome. In this case I've been manipulating the Arc-Black Theme with the following file for a while:
usr/share/themes/Arc-Black/gnome-shell/gnome-shell.css
. However, I haven't found any line of code to change the text or background color of the notifications.
Note: The following picture shows what happens in the notification panel, but, it's the same case for the pop-up system notifications.
You will need to add the following selectors to
gnome-shell.css
:Hope this gives you what you need.