At the moment, the dark mode toggle is in the footer. While I understand that some people may prefer this, I would like the option to put the toggle somewhere around the top of the screen, probably in the personal URLs. This is because I find that it is inconvenient for people to try to find the toggle when it's placed in the footer, since on long enough pages, you would have to scroll down to see it. Being able to have it in the personal URLs would mean that people wouldn't have to scroll to find the toggle.
I think that a good way to do this is by having a config variable, named something like $wgDarkModeTogglePosition, that would configure whether the toggle is placed in the personal URLs or the footer.