It's not CSS, it's basic primitive HTML. The MediaWiki table syntax is very close to HTML tbody/td/tr tags, close enough to intermix. The attributes go straight through, eg || bgcolor= becomes <td bgcolor=>. I don't do CSS. I hate CSS.
Use of attributes is part of the table scheme, since there aren't any substitutes. Border= is essential, to get a table with or without lines. Also, we need align=, valign=, rowspan=, colspan= etc.