You are on the right track and this is about as far as WP gets you.
WordPress does not have official style guides. There are some unofficial efforts to create one now and then, but they tend to wither and only sporadically maintained.
The practical (necessary) approach is to study markup of most current version, use it as much as possible, and get the rest done with custom CSS.
In your case if WP doesn’t have a native case of table in such context (I don’t think it does) you will have to adjust it with custom CSS. Always be careful to only load your CSS when needed and that it doesn’t interfere with the rest of admin.