The Book of CSS3 - A Developer\'s Guide to the Future of Web Design (2nd edition)

16

Values and sizing

Much of CSS3, from its many new selectors

to layout and font properties, is designed to

give you more granular control over presenta-

tion than was available in CSS2.1. That control will

be even more evident in this chapter, as I introduce

new value functions and units, as well as methods to

calculate dimensions automatically.

Relative Length Units

In CSS a relative length unit is one whose value is relative to another prop-

erty. The two relative units in CSS2.1 are em, which is calculated from the

font-size property of an element, and ex, which is calculated from the

x-height of the element’s font (see “font-size-adjust” on page 56).

CSS3 expands the range of relative units, which are no longer relative

solely to an element’s font size. The new units are defined in the Values and

Units Module (http://www.w3.org/TR/css-values/).

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