Add styling for definition lists

Definition lists are supported on the site, but could use some styling work:

The list items should be indented a bit more, like this: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/dl

Related links

• https://www.markdownguide.org/tools/hugo/
• https://www.markdownguide.org/extended-syntax/#definition-lists
• Related to Overhaul Security Report Ingestion Documentation (gitlab-org/gitlab!116185 - merged) where the idea came from