This is an alternative version for xfwm to match Obsidian 2 GTK theme (the default blue buttons on dark background). I created this one because xfwm default decoration from Obsidian 2 theme (https://www.pling.com/p/1173113/) has small buttons and size compared to the size of its CSD (client-side decorations) in GTK3.

So I created this version with a border that doubles the size, and buttons that imitate CSD style. Now GTK3 with CSD and the rest of apps look more alike in XFCE.
I have learnt that xfwm does not manage transparency very well. You'll notice that in external borders of round buttons: they lack antialias. The alternative would be to draw the button without transparency, extending all the height of the title bar. I've decided to keep the SVGs, though.

Anyway, When XFCE will also switch to CSD in the near future (see https://wiki.xfce.org/releng/4.16/roadmap/general_ui/csd)

I'll also say Obsidian 2 is a skeuomorphic design (just using this word here so anyone searching for this can find this theme).

Thanks @MADMAXMS for the wonderful Obsidian2 themes!

changelog:
1.0 initial release
1.1 added a proper prelight status to menu icon.