I would like operating systems, browsers and websites to globally support a "night mode" where a dark background is used. Especially with the proliferation of mobile devices, people increasingly use technology in low-light environments. As it stands today, I have to add external stylesheets to websites to get this effect, and if I want to toggle them, I have to toggle each one manually. It's similar, but worse for Android apps because the app itself has to support themes.
I find having a significant portion of the screen white when my eyes are relatively dark-adapted uncomfortable, even when the brightness is set fairly low. I find a dark background with light text very preferable under those conditions. I do not care if there is research suggesting I should not have this preference.
From talking to others in person and online, I get the impression that my preference is very common. Android was supposed to get something resembling this, but the feature has been dropped or delayed.