Breeze Darker is a GTK theme to match my Breeze Darker Plasma color scheme.
I have only used this theme on KDE Plasma and can confirm it works great with my Breeze Darker Plasma color-scheme.

Wallpapers are from Charlie Henson:
https://www.opendesktop.org/u/charlie-henson

Set look and feel to Breeze
Install color scheme
Install Breeze-Darker GTK theme
Set the themes. You will have to select Breeze Darker in Kate

Lots of screenshots here:
https://github.com/freefreeno/Breeze-Darker-KDE-color-scheme-and-GTK-theme-with-icons