I can’t seem to figure out where this is done?
From the docs …
You can set specific styles for each element nested in a rich text, like headings, lists, links, etc. You can do this before you connect your rich text element to a rich text field. Learn more about styling elements nested in a rich text element.
You cannot style elements nested in a rich text element when it’s connected to a rich text field. First, you need to remove the connection, style its elements, then, connect it again to the rich text field. You can remove the connection by unchecking the “ Get text from” under Inner Text Settings..