Upcoming builds of the 'Redstone 4' early development branch of Windows 10 will feature Fluent Design System elements being incorporated to the Settings app. As development of 'Redstone 4' progresses, we can expect to see more Fluid Design elements being incorporated in key areas of the user interface and inbox apps.
https://www.notebookcheck.net/Windows-10-Settings-app-to-get-some-Fluent-Design-makeover-in-Redstone-4.260284.0.html