I can change the manager appearance with custom css, but, I think, it's something that should be by default.

.txt file:

other text extensions:

Thanks, I'd forgotten about this, since I was using a separate user_style to invert text colors in dark mode. Using a user_style offers better control over text color display, since text (or html) files are displayed in an iFrame, which the script can't interact with. I can invert the iFrame, which is a coarse solution, since html files will have all their colors inverted as well. But I'll look at it again.

Updated. If I open, for example, a .html file and then a text file, for a brief moment I see the .html page with inverted colors. Seems like the css filter doesn't wait for the new iframe content to load.

Yes, I noticed that too (it's noted in the version notes). I did experiment with hiding the current iframe before loading the next content, but that was worse. I have a feeling that using a user_style to apply the dark mode would prevent this, but I will continue to look for an in-script solution.