I gotta admit, I didn't love the new Steemit UI design when it was released, but as soon as I saw that "Toggle Night Mode" option, I loved it. One thing I'd like to point out is trying to view replies to your comments while in night mode, notably that it's impossible to actually read the reply:
The best solution is probably to just change that off white/yellow (which works well on "day mode") to a darker color that's just slightly lighter than the surrounding grey of the night mode)