After a bit of searching, I found in the release history that multiple pipe-separated CSS class names can be specified for conditional row styling: https://dbfront.com/releasehistory#v1.2.0.0343
(side note: this info is missing from the help page on the feature: https://dbfront.com/table-row-styling)
This works great and currently only appears to apply for table row styling.
It would be convenient to have this feature in all areas of dbFront wherever a custom CSS class can be specified.