To Enable The Dark Theme In Windows 10 Follow this Steps:
For Windows 10 Professional & Enterprise Users:Step 1: Type Regedit in the search bar and open the Registry
Step 2: Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize
Step 3: Create a new DWORD value and name it “AppsUseLightTheme”
For Windows 10 Home Users:
Step 1: Type Regedit in the search bar and open the Registry
Step 2: Go to HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize
Step 3: Create a new DWORD value and name it “AppsUseLightTheme”
It didn’t work?
Open the Settings app and go to the Personalization group of settings. In the Color tab, toggle the color accent color switch a few times. The theme should change with the first switch.