If you have a Wikipedia account you can set this theme as your default theme in your account preferences without having to visit the m. domain.
Sidenote, if—like me—you actually prefer the desktop theme, and would like the opposite: to use it on mobile. There is a mobile-friendly version of it in the works, but not yet available. You can try the in-progress version on your mobile here: https://test.wikipedia.org/wiki/Main_Page?mobilaction=toggle...