HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes

Create new directory under themes “Personalize”
add a new dword(32)
AppUseLightTheme
set the value to zero

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes
Open personalize directory if present
change the value of the dword – AppUseLightTheme
set the value to zero. by default it will be zero.