Theme content packs allow you to add backgrounds, skins, and ringtones to the mobile phone that can be used with the built-in Themes app.

Each background or skin must have both a <name>.png and a <name>_landscape.png file, and they should be the same size as the phone, portrait and landscape. 

Each ringtone must be a 16-bit PCM WAV file.

Backgrounds go in the content packs assets/backgrounds folder, skins go in its assets/skins folder, ringtones go in the assets/ringtones folder.

You can also now include events in a theme content pack, which allow NPCs to reminisce over seen events during a phone call. Event files go in assets/events. A content pack with events you can use as a templete is the one for Blanche the Librarian, available in the optional files list for that mod.

You can use the example theme content pack found in this mod's optional files section, and just replace the files in the respective folders with your content. Then edit the manifest.json file, especially the UniqueID, to be personal to your content pack.