It's funny to me that dark themes seem to be the preferred theme type in online discussions, because in practice, most people I know prefer a light theme on a monitor set to high contrast and relatively low brightness in a well lit setting. I too prefer that, as it seems to reduce (eliminate?) my eyestrain after hours on the computer.
I think it depends a lot on age and level of eyesight. I've never once felt eye strain from looking at a dark theme, and if a room is even somewhat dark then a blindingly white screen gives me a headache. I can always fiddle with my brightness as needed for different situations, at least on my phone, but that's kind of a pain. On a desktop monitor it's usually a significantly bigger pain.
If you do not need coloured text on your web page (due to coloured diagrams, colour coding, etc) then please do not specify colours at all. (If you do need colours, then ensure that all of the colours are specified.)
I hate it when the font color is set but not the input background. On computers with dark themes this can result in black on black text. There are workarounds in Firefox and I use them but this cost me more time than necessary.
> If I have to adjust my monitor brightness to be okay with reading something there's a major issue.
Yes, but the issue is with your monitor brightness or your ambient lighting, not the content. I tune my monitor for use at night with the lights on and as a result, #000 on #FFF is perfectly comfortable at all times. There's rarely a good reason to use a PC in complete darkness and I can't think of any reasons to do it in your own home.
I think that's the key point there. Light themes are good in light, but bad in dark situations, and vice versa. "Most" people prefer light, because they use their computer mostly in the light. Many programmers etc. prefer dark because they use their computers late in the dark a lot.
These are basically two "modes" of use, but software has been treating this as a preference, rather than a mode switch.
Through a set up of PowerShell/Bash scripts, I now have global dark/light mode switches on all my devices and I feel like this is the first time I can really use them effectively in all situations. Light when there's light, dark when there isn't. I even switch on the train as it goes through a tunnel. IMO, this is how it should be used, not as a set-and-forget preference.
The problem with bright themes used like that is that "high" contrast is still not very high at all, unless you go for OLED technology - but then you'd want to use green-on-black anyway to minimize wear on the display elements.
