In many non-fiction or technical books, there are sidebars (text offsets). My preferred way of handling these is to insert a pair of red horizontal dotted line at the start of the sidebar and another pair at the end.
The way I accomplish this now is by editing the EPUB in Sigil and inserting empty div or p tags, and then styling them with border properties.
This is essentially how Microsoft Word handles these using their borders feature when saving the document as an html file.