As a beginner, I had no idea why one would choose percent over em’s, or pixels over percents to specify text size. You are hereby witnessing my breakthrough to intermediate, with this article on text-sizing strategy!
Basically, you want to stay away from absolute sizing methods, so that those who are interested can use their browser to resize the text. Sounds smart, and if done from the beginning of the design, easy.
Check here for a visual introduction to the almost infinite variability in text rendering between common browsers. Note to Owen: Very pretty presentation– Add me some Firefox 3, next revision!
PS: Sitepoint also had a great article on font sizing, and jontangerine spilled this Pixels to Ems Conversion Table for CSS. Handy McDandies!
The point is surely to provide a method for resizing fonts. Setting everything using relative font sizes can be problematic. for some designs.
I quite like to provide a baseline font size with an absolute measure, and then use a widget (server side best for accessibility) to allow users to pick a font size of their choice, overriding the baseline style sheet.
Store their preference in a cookie and they’re happy.
Of course, now Firefox 3 and IE 7 are zooming, rather than doing a strict font resize, (which works great on our site by the way), everything can grow – fonts know their places in boxy designs, because the boxes grow with them.
Of course, that doesn’t save the users of older browsers, but its an interesting development. If zoom becomes a more universal standard, will designers be off the hook?