If you've ever wanted a bit more Master Chief flavor with your Mahjong or Solitaire games, Microsoft has good news for you. Halo themes are now available for the Microsoft versions of the two games.

The themes are free for all players and were designed by Halo developer 343 Industries. For Solitaire, which is on PC and mobile, the cards get an overhaul, with all of the face cards now showing Halo characters instead of the normal Jack, Queen, and King. The gems in Mahjong, which is only on mobile, are changed to look like Halo's multiplayer medals.

It might seem weird on face for Microsoft to target its casual games like this, but Solitaire and Mahjong are enormously popular. Solitaire in particular is comically massive: During Microsoft Solitaire's 20th anniversary celebration last year, the company announced that over 35 million people still play it each month. Many of those people probably don't play many other Microsoft games yet, despite already being connected to the Xbox ecosystem. As a result, it's a big pool of people to market Microsoft's exclusives to--and these themes are a straightforward way to raise awareness.