3,038 questions
Save "System Theme" to app data and on app initialization, do this:
auto DefaultTheme = ref new Windows::UI::ViewManagement::UISettings();
auto uiTheme = DefaultTheme->GetColorValue(Windows::UI::ViewManagement::UIColorType::Background).ToString();
if (uiTheme == "#FF000000")
{
App::Current->RequestedTheme = ApplicationTheme::Dark;
}
else if (uiTheme == "#FFFFFFFF")
{
App::Current->RequestedTheme = ApplicationTheme::Light;
}