Goto the “Quick Launch” (Ctrl+Q) and type “using” and press Enter.
Then change the following setting:
It’s an annoying default setting, I have no idea why Microsoft chose that, it goes against all previous standards that I’ve ever seen.
EDIT:
Thanks to Oskar we have a reason:
The reason for the change in default behavior is due to the fact that
Windows App Store applications prefer to have ‘Windows.‘ at the top
of the file rather than ‘System.‘