I believe what you're looking for is a combination of two customizations:
- Adding a custom formatting button via Redactor's
formattingAdd option. Config example below! 👇
- Custom CP CSS rules to style the list in the Redactor field as your editor expects it. The strategy for this is up to you, but Double Secret Agency has the simplest method via their Control Panel CSS plugin.
- Of course, front-end styles to match.
Redactor will expect something like this for your custom formatting rule:
"buttons": ["italic", "bold"],
"title": "Create Letter",
(This was adapted from Craft's built-in
Keep in mind! This will add a new option to the "Formatting" drop-down menu (i.e. where the headings,
blockquote, etc. might appear), not with the List options. I'm not sure exactly how to adjust the options in that menu… 😬
The answer from @user3788089 is about 99% there—I think the only new thing above is re: styling within the control panel. ✌️