This is vertical navigation on the right hand side or top of the page on desktops. It’s used alongside content and contains sibling pages. When a sidebar navigation isn’t used on a content page, the content should not extend further than the main-content width.
The mobile version of the sidebar is collapsed and at the top of the page, this is achieved using the flex order -1. It is a continuation of the revealables pattern
The title of the section nav, that groups the list of sibling pages needs to link back to the previous page.