…or with the words of Simon & Garfunkel: Hello darkness my old friend! 
Moin @all.
We specifically decided to add a toggle for those who prefer a dark theme.
As we had to find out, this only becomes active if you have selected a corresponding dark theme in your user settings.
Basically, the switch is located at the bottom left.
To activate it, do the following:
Click on your avatar in the top right > click on the symbol for your personal activities at the bottom and then on settings.
Then select a scheme for the dark mode on the “Interface” tab under “Colour Theme”. Now click on “Save changes” at the end of the page. After that, the page refreshes itself and the toggle becomes active.
Cheerio
Frank
