Most of the Qubes OS UI in dom0 is now Qt5 based and doesn’t by default adhere to the selected theme, which is especially annoying when using a dark theme. Luckily this can easily be remedied by installing
qt5-qtstyleplugins
and exportingQT_QPA_PLATFORMTHEME=gtk2
(e.g. in/etc/environment
).
From my post in another thread.