I've been using the MiG-21 a lot lately, so I was getting a bit bored of the MiG's default theme. I replaced the wallpaper, the loading screen, and the background music. It's packaged in OvGME format, so that I can easily change themes as the mood strikes. It does not impact the multiplayer IC, since its files go into your /Saved Games/ folder. To use it you will have to select the USER THEME.

Credits: 
Wallpaper photo by Steve Knight.
Loading photo from alphacoder.com, if anyone knows its origin please let me know.
Music by Laura Brehm, https://www.youtube.com/@laurabrehm