lucy24 - 11:48 pm on Jul 14, 2012 (gmt 0)
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w3 CSS index [w3.org]
(Do not be misled by the address: That's 2.1, not 2.0.) Once you are there, you can zip along to, for example, http://www.w3.org/TR/CSS2/fonts.html#propdef-font-size [w3.org]
Note that "absolute" has two different meanings, one that you want and one that you don't want. The one you do want is the one shown in the table. These sizes are defined relative to the user's default size. They're called "absolute" because they are not affected by the size of surrounding text.
But note cautions about the exact proportions. That's why I generally prefer to use percentages-- but those are "relative" sizes. If there isn't any surrounding text, as in a free-standing header, "absolute" and "relative" are essentially the same. That is, "medium" = 100%.
What the user sees when they zoom depends on the browser. Nice browsers have an option for "zoom text only" so the overall display remains as intended but the print gets bigger. Invaluable when reading a site in 9-point grey Courier.*
* Unfortunately I am not making this up-- and it's a blog by someone I like :( Adding insult to injury, the writer is my father's age.