In summary, I prefer dark themes and my QT based applications weren’t matching this preference. I’m using Xfce.
After some digging around, and this video, here’s what I did.
$ nano ~/.config/Trolltech.conf
[Qt] style=GTK+
$ sudo pacman -S qt5-styleplugins
$ sudo nano /etc/environment
QT_QPA_PLATFORMTHEME=gtk2 QT_STYLE_OVERRIDE=gtk2