Switched to Opera after a while of chromin n foxin, and obviously one of the first things is to look for a good general dark mode. So I browsed the search results and apart from the usual suspects (of which some are ok but none truly ideal) this one stuck out as a (to me at least) new contender. – Usually not a frequent reviewer of extensions, but the first impressions are super in terms of tweakability, results, and speed, plus the developer seems to be responsive and helpful (see below), so I recommend you guys give this one a try!
Don't install from here though cause for some reason Opera has problems with their addon updating process. So everyone go to https://chrome.google.com/webstore/detail/eimaelgbclmdoeimifebaagealdkjmki/
and install the chrome version. You may have to get the "Install chrome extensions" addon first.
Cheers and stay dark, folks