Pseudo-classes and Pseudo-elements

Pseudo-classes and pseudo-elements are special "classes" and "elements" that are automatically recognized by CSS-supporting browsers. Pseudo-classes distinguish among different element types (e.g., visited links and active links represent two types of anchors). Pseudo-elements refer to sub-parts of elements, such as the first letter of a paragraph.

Rules with pseudo-classes or pseudo-elements take the form

selector:pseudo-class { property: value }

or

selector:pseudo-element { property: value }

Pseudo-classes and pseudo-elements should not be specified with HTML's CLASS attribute. Normal classes may be used with pseudo-classes and pseudo-elements as follows:

selector.class:pseudo-class { property: value }

or

selector.class:pseudo-element { property: value }