If you use Firefox, there's an add-on called "Dark Mode" which will change the appearance of any website. It works on SB, I'm using it right now. There's other add-ons that let you customize everything you see on a site, so if you wanted teal text on fuscia background then you're a moron. Still, you can customize websites to your heart's content with plug-ins. Might be doable on chrome, but I don't know since I don't use it... and if you use ie/edge you deserve what you don't get .I'll go back to BB if it means I get dark mode though.... Yeah @The Chairman , i'm a squeaky wheel!
That said, having native dark mode will be nice. Having user configurable L&F would also be nice.
https://addons.mozilla.org/en-US/firefox/addon/dark-mode-by-albert-inc