Spending one’s Christmas with family really reminds one of that not all web users have good eyesight.
There have been hundreds of articles written on accessibility in web design, and the w3c’s web accessibility initiative (http://www.w3.org/WAI/) is a good place to start for super accurate information on the subject.
As a typographer, I always used to use the EM measure to indicate spatial relationships by proportion. A long dash was an EM dash, leading in Bodoni was one and one-third EM and so on. The idea was to preserve the ‘character’ of a piece of design by managing the distances between parts of the composition in a manner that was independent of any size measurements.
The EM measure appeared in CSS a few years back and I tried to start using it then (what was it Andrew, 1997?) but came up against design requirements from clients. It was impossible to get the type on screen to display at a predictable size, and most clients wanted to mimmic the 9/11.5 point size of their brochure. Of course all of this was ridiculous - creating content for any specific rigid device description is just plain silly and defeats one of the Internet’s greatest features, its lack of platform dependence.
Anyway, to cut a long story short, this is a web log - no client! I can do what I like:-) So the fonts on this page are going to be experimented with as a learning exercise. Today’s style sheet specifies a base font size of 0.8EM or in other words, just slightly smaller that the standard size for a given environment (in theory).