font-size | NN 4 IE 4 CSS 1
| Inherited: Yes
Determines the font size of the element. The font size can be set in several ways. A collection of constants (xx-small, x-small, small, medium, large, x-large, xx-large) defines what are known as absolute sizes. In truth, these are absolute as far as a single browser in a single operating system goes because the reference point for these sizes varies with browser and operating system (analogous to the old HTML font sizes of 1 through 7). See Figure 11-4 and Figure 11-5 for size comparisons viewed on the same video monitors. But they let the author have confidence that one element set to large is rendered larger than another set to medium.

Another collection of constants (larger, smaller) are known as relative sizes. Because the font-size attribute is inherited from the parent element, these relative sizes are applied to the parent element to determine the font size of the current element. It is up to the browser to determine exactly how much larger or smaller the font size is, and a lot depends on how the parent element's font size is set. If it is set with one of the absolute sizes (large, for example), a child's font size of larger means that the font is rendered in the browser's x-large size. The increments are not as clear cut when the parent font size is set with a length or percentage.

If you elect to use a length value for the font-size attribute, choose a unit that makes the most sense for fonts rendered on the output medium, such as pixels (px) for screen display and points (pt) or ems (em) for printed output. Em values are calculated relative to the size of the parent element's font size. Finally, you can set the font-size to a percentage, which is calculated based on the size of the parent element's font size.

Some browsers hijack your best efforts at precisely sizing fonts, using their own (or user) settings to establish a "medium" size. That is why many designers prefer to rely on the relative-size constants for their font-size specification schemes. This choice means giving up a level of control over rendering from one browser and operating system to the next, but attempting too strict control on uniform rendering generally leads to utter frustration.

CSS Syntax
    font-size: absoluteSize | relativeSize | length | percentage
Value
For an absolute size, one of the following constants: xx-small | x-small | small | medium | large | x-large | xx-large. For a relative size, one of the following constants: larger | smaller. For a length, see the discussion about length values at the beginning of this chapter. For a percentage, the percentage value and the % symbol.
Initial Value
medium (for BODY element); the parent element's font-size value (for all others).
Example
    body {font-size: 14pt}
    p.teeny {font-size: x-small}
    em {font-size: larger}
    span.larger {font-size: 150%}
Applies To
All elements.
Object Model Reference
    [window.]document.getElementById("elementID").style.fontSize