So that should be taken care of, I would think, but alas, apparently not. Always thought imbedded CSS would overwrite global CSS.
However, the iframe solution worked with a minimum of hassle, so I think I will stay with that solution for now. Especially as we might be adding a lot more of that kind of "stand alone" HTML code.
Actually I found out, that WFsections couldn't handle the insane amount of characters generated by Excel -> HTML converter. It cut off the text at one point. I will have to look into it a bit more, before I can say anything conclusive. Might be a problem with Windows clipboard, but I doubt it.