
There was major issues with messed up minimise/maximise/close buttons.
I used BIB3 theme, you can browse Deviantart or other resources for any dark theme you want, but BIB3 seems to work great for my goal of total Dark Mode. It is not possible to achieve adequate Dark Mode on unpatched system, I'm afraid ( there is one attempt at this, using high-contrast theme, but due to very poor Microsoft's High Contrast implementation, its very limited and almost unusable). This is only possible with theme patch, however. And it probably will look better than Windows 11. At first I thought it's not possible, but it is. Well, now I can give myself and others a definitive answer of how to do it.
I went on a few tangents, however, like learning a bit of assembly and injection into other processes, a bit of JavaScript/CSS to style Firefox too, made custom low level API registry access library, etc. I was focused on this all this time, almost all day long. I can't believe that 2 months actually passed since I embarked on the quest to make Windows 10 100% Dark Mode, in every window in the system.