plone tableless and negative margins
hooray! I’ve finally understood why the plone tableless skin uses negative margins in the CSS - it is to get round the inabilty to specify a width of something like (100% - 16em) in CSS.
I did start to write up a full explanation, but then closed my browser before saving it, which is just as well, because it is much better explained by this article.
Hopefully now I understand it, it won’t spring apart like a clowns car the second I adjust some padding 