TBH, I'd be surprised if IE6 actually used CSS internally for laying out the majority of HTML elements, so what you're looking for may not even exist.
The W3C have a sample stylesheet in the CSS2 spec (http://www.w3.org/TR/CSS2/sample.html) which "describes the typical formatting of all HTML 4.0 ([HTML40]) elements based on extensive research into current UA practice" - copying that into a stylesheet is probably the best you'll do.
