Microsoft released Windows 10 Build 18277 to Insiders in the Fast ring just a few days back with a few noteworthy changes and fixes. Interestingly, Build 18277 has a subtle UI refreshment that Microsoft did not talk about specifically- OneDrive on the taskbar of your PC now has the dark theme if you are running the latest Insider build.
As Microsoft has just introduced the feature things are bit rough here so don’t expect this thing to be super-smooth. You might also not see it at the first go, in order for this to get a Dark Theme you might need to switch to the Light mode and then again back to the Dark Mode. Not sure where to turn on the Dark Theme/Light Theme? It follows your system theme under Settings > Personalization > Colours.
Microsoft has to face a lot of criticism in the past for not implementing Dark Theme throughout the operating system and some its stock apps. On the other hand, MAC OS nailed the Dark Theme on the very first attempt. In Microsoft’s defense, one can argue that Windows 10 is a work in progress and always will be like that, so any feature that gets released without the final touch is what Windows 10 is all about.