If, like me, you have been irritated by QT apps rarely respecting dark themes (or any GTK themes), here is a link that will allow you better alignment of your QT apps (like the MX Tools suite, calibre, Virtualbox) with your dark GTK theme. I know the article says it’s for VirtualBox (and it is) but it also fixes all your other QT apps at the same time. 
I just wish it were perfect, but remember: “better is never to be confused with good….” 