I have just started to customize my Ubuntu a little bit and found the Arc-Dark theme to be exactly what I am looking for.
There are some small things though.
The color of the calendar on top is still white, and the font of the notifications and inside the calendar are off. This is what it looks like right now:
I would like to see the calendar being the same darker color, and maybe having the day numbers font in white.
Also the font color of the search bar is off. There is text, but it is just as dark as the background.
It's only visible when you hover over the search bar.
How would I go about changing/tweaking these things? Or did I do something wrong during the installation?
UnKNOWn has answered my question (accepted answer).
The css-file was, in my instance, found at
/usr/share/themes/Arc-Dark/gnome-shell/gnome-shell.css. I made the small changes to
.search-entry, saved the file (with sudo rights) and reloaded the theme by simply re-applying it with Gnome-Tweaks!