Each Stack Exchange site should provide users the option of using a dark site design/theme. Why is this feature missing? The major IDEs are already a letdown regarding dark color schemes.
I think this is a great suggestion. ProjectEuler.net has implemented this effectively, naming it Lights On / Off.
If you're using Gnu/Linux and have compiz installed, you can always invert the colors of your active window (look for "Negative" in the CompizConfig Settings Manager).
Without compiz there is an alternative solution via
xcalib -invert -alter.
It's how I circumvent this strange so-white-I-bleach-your-eyes-out-background-dogma that's cursing the interwebs.
But anyhow: Yeah, a supported dark theme would rock.
I see a couple problems with doing this.
First, there currently is no way to change to any different theme on a per-user basis. So that's something that would have to be implemented. I don't think it would be all that difficult, really, but still that's an non-trivial amount of work.
Second, the themes would have to be populated. Who will create these themes? Will they be user submitted? If so who would approve them? Would there be safety potential concerns? (I'm not a front end guy, so I don't know, could someone put 'bad things' in a css?) If it's internal would this the next intern's project or something?
Third, the themes would have to be maintained. When there's a formatting problem, we'll have to ask "What browser, what SE build, oh and what theme?" It's another piece of the puzzle that would just complicate things.
Now, who doesn't like the idea of customization? I think it's great when there's multiple themes. Stack Overflow has so much orange I feel like it's Halloween all year round!! But honestly, I think the costs far far FAR outweigh be benefits we would receive from a feature like this.
It's possible to have alternate CSS themes for sites — it's even common to have alternate themes designed specifically to support printing — and browsers often (always? I dunno) have an built-in mechanism for selecting between the themes at the user's request. I certainly remember using this with Firefox on a number of sites, but haven't tried for a while to be honest. However, that doesn't mean that it is necessarily a wise thing to do. In particular, the alternate theme would need to be developed and maintained; surely that developer effort would be better spent elsewhere?
If you really want your own style, force your own stylesheet that overrides key things like colors (you probably want to leave the layout the same though). I'm sure that's possible, and it puts the cost of maintenance squarely on those who really care (i.e., you).
Came here and realised that this still isn't a thing! You can use Stylish to either create your own dark theme or there are a number of dark themes available (I don't think they're that great but I prefer a slightly broken dark theme to the current white theme).
Would definitely prefer it to be officially supported, but this is a workaround if you're desperate!
Note that IDE is not a webserver, IDE supports customization of colors initially.
Some time ago I've made a custom CSS for SO site for use with Stylish/Stylus plugin
(not dark, but you can find dark themes).
So I know that the SO's CSS is (or was at that time) really complex and that makes things hard.
(It's main CSS file is ~5000 lines (400kb file), i.e. 10 times bigger than a CSS should be).
Specifically with a dark theme, it would be hard to adjust all corners of this site, there are many images and colored backgrounds. Too many elements would require manual adjustment.
If speak about feature requests towards themes, I'd wish first that the CSS reduces it's complexity radically. This would allow easy customization via plugins and solve the issue once for all and for everybody.
Subjective things & opinions
Some people want a dark theme, some people want e.g. better fonts, layout, ans so on. "Dark theme" does not mean anything specific, there can be many different dark themes, why you think the one you like would be better than some other "dark theme"?
And finally, I just think all these dark themes is just a gimmick (or exceptionally a technical requirement e.g. for improving battery life or working in dark environment). Moreover as someone who understands things from UX and readability issues, I'd just recommend to always stay with black text on light background when you have textual content. In other words, making dark theme for an informational site is initially a bad idea. It might be ok for Youtube or online cinema interface, but not for text-centric media.