Scrivener already has the necessary ingredients to mark text that should be formatted using fancier design tools, that it does not itself support in the editor or via compile settings. In short you are very rarely limited to what Scrivener itself can do in its necessarily simple text editor, thanks to its extensive and powerful style system:
-
For ebooks: note there was some initial confusion as the OP was asking about “sidebar formatting”, but it was later confirmed they meant call-out boxes. Scroll down a bit to a follow-up post I made with an amended example projects that implements that design.
-
For print: note this thread starts out with a conversation on using Scrivener’s more advanced compile mechanisms for sophisticated formatting, including LaTeX, but also encompasses conversion to other formats as well, such as ODT and DOCX. The post I linked to here though goes into how this should be done if you’re using Scrivener like a word processor instead of a Markdown editing platform.
- What that post doesn’t point out is that you needn’t modify your call-out box styles over and over, every time you compile. The preferred approach is the same you would use with Markdown generated word processing content, and is described in this post, in overview, with a link to more expanded instructions elsewhere.
- This much longer post goes into the advantages of LibreOffice over Word, as a complimentary tool with Scrivener, and how one can go from rough styled text to a nearly complete layout and design in a matter of seconds, after compiling.