Unfortunately the editor cannot be extended to include additional buttons, so custom styles like those provided in our themes must be added using the Source Code view. To apply a custom style to an element using a class name:
Create a new article or edit an existing one within Zendesk Guide.
Click on the Source code button () in the editor toolbar.
Locate the heading, paragraph or other element that you’d like to style and either add a class to the existing list of class names or create a new
classattribute. For example, a standard paragraph can be transformed into a styled note callout using the
<p class="note"> This is an example of a standard note available in all themes. You can apply this style to any content by simply applying the <code>.note</code> class name to a paragraph or container element. </p>