I’m using Plasma 6.2, and I have a big monitor, with some tiled windows.
It’s not easy to see clearly which is the active window with the Breeze dark default theme.
For example, Pop OS! displays an orange border around the active window.
I’ve tried to download other themes but it fails to.
You can do it with Klassy window decoration. There used to be another way by adjusting the colorscheme, but I simply can’t remember how it was done.
Anywho…Klassy.
+1 for klassy.
Alternatively one could also set up the older oxygen windeco and use it’s active glow
Thanks for your recommendation.
I have already installed klassy.
Now I have to experiment with it.
It isn’t very intuitive with Klassy for example to configure a different background for the titlebar of active windows.
I must try oxygen.
I use “Dim inactive” under Desktop Effects in settings. It makes the windows that are not active darker.
Dimming is not very usefull if you’re tiling stuff.
I remember now. A small hack I used back in the days was to add two lines to the ~/.config/kdeglobals file, section wm. That way you could color the frame. Dunno if it helps really and dunno what plasma 6 gives.
But, for example, two windows ( standard breeze) without the “hack”.
And with…
The width of the frame is set in the window decorator.
It’s just some hack and, personally, I prefer the “non-intuitive way” Klassy handles stuff. 
