ChatThemes

ChatThemes adds a button for change themes on the chat at the bottom of Rail.

Installation
For site-wide add the following code to MediaWiki:Chat.js on your Wiki, for personal use add this to your Special:MyPage/chat.js:

Customization
This script require a list with names and classes for themes, by default the script includes a nightmode theme. You can customize it, following the next example: Seems like JSON.

The class will be included to  (body class) following the order of the list that you defined.

CSS
Once injected the class into the body class you can customize the chat following the injected class, for example: