The CSS2 :hover pseudo-class

The newly released Cascading Style Sheets Level 2 Proposed Recommendation (CSS2) includes a new, dynamic pseudo-class: hover:

"The :hover pseudo-class applies while the user designates an element (with some pointing device), but does not activate it. For example, a visual user agent could apply this pseudo-class when the cursor (mouse pointer) hovers over a box generated by the element."
Read the complete dynamic pseudo-classes specification

When we apply the :hover pseudo-class to an element, the CSS properties declared in the pseudo-class will take effect when we mouseover the element, and cease when we mouseout. It is like changing the class of an element upon mouseover and changing back to the original class on a mouseout. See Doc JavaScript's Text Rollovers for a discussion of dynamic class change to create rollover effects.

By using :hover, however, we can create dynamic class changes without the need for script and with minimal page HTML intervention.

Currently, :hover is implemented only by Explorer 4, and only for the A element, and only when it is a link (contains HREF= attribute).
Read the Microsoft documentation in the Internet SDK

Defining :hover

The complete DHTML Lab site uses :hover to change the normally red links to blue, upon mouseover. All we need is a single line in our STYLE:

<STYLE TYPE="text/css">

    A:hover {color:blue}

</STYLE>

If we include A:hover {color:blue} in an external stylesheet, then any page that uses the style sheet will have blue text rollovers for links. :hover changes only the properties declared in the :hover definition. All other properties remain the same. If we were to use this STYLE:

<STYLE TYPE="text/css">

    A {
        color:red;
        font-family:sans-serif;
        font-weight:bold;
        font-size:14pt;
        text-decoration:none;
    }
    
    A:hover {color:blue}

</STYLE>

The result would be:

  DHTML Lab   (mouse over link)

The :hover pseudo-class can also be applied to classes of links or to unique instances.