This is suggested pretty often. I remember Chedburn shooting the idea down once, but I can't seem to find his response from a quick search. It has been a long time since that though, so perhaps he would be willing to reconsider. This suggestion also never seems to get very far before being lost in the clutter.
I'm still very much in favor of the suggestion, however. I use the dark theme on everything that allows me to, reddit, youtube, twitter, discord, twitch etc. There are plenty of examples of how well this works from very popular websites. The dark theme really helps prevent eye strain for someone like me who spends the majority of their day looking like a screen. Often times I find torn to be too bright, especially if I'm in hosp. Right now, there doesn't seem to be any scripts that do this well.
Good luck! Maybe this will be the one.
A few previous times this was suggested:
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