I am not entirely sure what exactly this style is. You can take a look at the Styles article
in our documentation where it is explained how to work with styles in RadRichTextBox. If this article is not helpful for you, please share more information about the style you want to create.
I hope this helps.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.