This is because for using the dark style, electrum needs the package
qdarkstyle (https://github.com/ColinDuquesnoy/QDarkStyleSheet). It
seems the package hasn't hit the Debian archives yet
(https://ftp-master.debian.org/new/qdarkstyle_2.8.1+ds1-1.html).
But you can use pip3 instead. The Debian electrum package depends on
qdarksytle < 2.7, so you could just do `pip3 install --user -Iv
qdarkstyle==2.6.8` and electrum should be as dark as expected :)
