Compact variant of my Adwaita-dark-xfwm4 theme. (https://www.opendesktop.org/p/1277456/)
Since you guys asked for it, I've reduced the titlebar size of non-CSD apps by 10 pixels.
It still looks largely consistent with GNOME's default Adwaita-dark theme (v3.30).
This gives CSD and non-CSD apps a fairly uniform look in XFCE.