These are specific feature from Pandoc (Pandoc - Pandoc User’s Guide) which are more than CSS classes.
Some classes on divs won't even translate directly to a CSS class, like the colum feature
https://quarto.org/docs/presentations/#multiple-columns
There is not full list of all classes on Divs that works built in, but everything feature that use some is documented.
However, regarding theming as you mention CSS and xaringan theme, there is a list of all SASS variables supported to quickly customize a revealjs theme Quarto - Reveal Themes