Use the aside element

The [MDN Web Docs](https://developer.mozilla.org/en-US/docs/Web/HTML) define the use case for the `aside` HTML element as follows:

> The `` [HTML](https://developer.mozilla.org/en-US/docs/Web/HTML) element represents a portion of a document whose content is only indirectly related to the document's main content. Asides are frequently presented as sidebars or call-out boxes.

We here at SBS use this quite a bit for sidebars, etc

This should also provide capability for admonitions like warning, hazard, danger, or caution.