Chapter 1. Values, Units, and Colors
In this book, we’ll tackle features that are the basis for almost everything you can do with CSS: the units that affect the colors, distances, and sizes of a whole host of properties, as well as the units that help to define those values. Without units, you couldn’t declare that an image should have 10 pixels of blank space around it, or that a heading’s text should be a certain size. By understanding the concepts put forth here, you’ll be able to learn and use the rest of CSS much more quickly.
Keywords, Strings, and Other Text Values
Of course, everything in a style sheet is text, but there are certain value types that directly represent strings of text as opposed to, say, numbers or colors. Included in this category are URLs and, interestingly enough, images.
Keywords
For those times when a value needs to be described with a word of
some kind, there are keywords. A very common
example is the keyword none
, which is
distinct from 0
(zero). Thus, to
remove the underline from links in an HTML document, you would
write:
a:link, a:visited {text-decoration: none;}
Similarly, if you want to force underlines on the links, then you
would use the keyword underline
.
If a property accepts keywords, then its keywords will be defined
only for the scope of that property. If two properties use the same word
as a keyword, the behavior of the keyword for one property will not
necessarily be shared with the other. As an example, normal
, as defined for letter-spacing ...
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