A style attribute is the name of a (usually) visible property of a piece of content on the page. An attribute such as color can apply to any element because that color can be applied to foreground content, such as text. Some attributes, such as borders and margins, can apply only to elements rendered as blocks on the page—they have a clear beginning and ending in both the HTML source code and in the layout. In their conservative approaches to claiming standards support, IE 6 and Netscape 6 promise full implementations of CSS1 (while both browsers support a lot of CSS2). To help you visualize the range of style options available as a common denominator, Table 3-1 shows a summary of CSS1 attributes grouped by category. You can find details of all CSS style sheet attributes in Chapter 11.

The syntax for assigning a value to an attribute is different from what you know about HTML attributes and their values. Assign a value via the colon operator (in contrast to the equal sign operator in HTML). A space after the colon is optional. The combination of an attribute name, colon operator, and value to be assigned to the attribute is called a declaration. To assign the color red to the foreground of an element, you could use either of the following simple declaration forms (colors may be specified many ways, as described in Chapter 11):

color:#ff0000
color:red

If a style sheet rule includes more than one declaration, separate declarations with semicolons:

color:#ff0000; font-size:12pt;

A trailing semicolon after the last declaration is optional, as is a space after the internal semicolon.

Notice, however, that unlike HTML attribute values, CSS syntax attribute values do not—and cannot—have double quotes around the values, except in rare circumstances (e.g., multiword font family names).

Defining a rule's declarations is only half the job. The other half involves identifying the HTML element(s) to which the rule applies. This is the job of the selector, which acts as a kind of label signifying the element or type of element to which a rule applies. In a simple case, you bind a declaration to a single element or a single type of element (e.g., all p elements, where the label is, literally, just p). The CSS standard also provides for additional ways of binding a declaration to a subgroup of elements scattered throughout a document (e.g., all elements sharing the same class attribute value). Finally, you can define exceptions to the grouping rules you establish in the document.