The styles we have seen so far are attached to element names (e.g., div), class or id attributes (e.g., .big, #wrapper), or position in the page structure (e.g., ul ul). Pseudo-classes are used to classify elements by other means. The syntax of pseudo-classes is element:class.
Currently, the best supported pseudo-classes all apply to link states. A link can have the following pseudo-classes:
a:hover - indicates the mouse pointer is over the link
a:visited - indicates the link has been visited
a:active - indicates the link is active (e.g., the user has clicked down on it)
If a:active precedes a:visited, then the rule for a:visited will take precedence. This means that, where there are conflicts, those properties defined for a:active will not be seen for visited links.