It's not a good idea to just stick with Windows 7 forever. In 2020, support will be dropped, after the operating system becomes 10 years old. This is assuming that support is not going to be extended like it was with Windows XP.
At that time, Windows 10, maybe even 11 will already be out.
Now, however, we have Windows 8.1, which works fine after installing Classic Shell and trashing Metro, even though I still hate the flat GUI. I've been looking into WindowsBlinds, by Stardock. It can change anything in Windows, and today, it just costs $9.99. It's been around for 15 years, and was adapted for each new Windows version.
I would seriously consider looking into this software; make a system restore point, and install the trial. At WinCustomize.com you can find lots of themes. If it's anything like KDE-Look.org or other Linux-related theming sites, half of the themes will be various various shades of black, or at least quite dark...
You can even make your Windows
look like a Mac if you're inclined to do so.