how to get windows dark mode code example

Example: windows detect system dark mode

RegGetValueA - gets a value from the registry (winreg.h)
use it to retrieve this key:
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize\AppsUseLightTheme
res == ERROR_SUCCESS && data == 0 = dark mode
otherwise = light mode (1 is light and fallback should be light)