❔ Using System Colors

Hi, I'd like to access the colors that windows uses for it's apps in order to allow theming for my app but I am having hard time. First picture shows the windows's dark mode with the top border using the WindowBrush color(which is supposed to be what file explorer uses for the background) yet it appears white. Second picture shows that file explorer(as well as my app) do indeed react to custom windows themes(Nord Darkest by niivu in my case). So what's the reason behind the light/dark themes not affecting these colors?