CSS3′s best features

The box-shadow property allows designers to easily implement multiple drop shadows (outer or inner) on box elements, specifying values for color, size, blur and offset.
Browser support is growing of late with Mozilla (Firefox), Webkit (Safari/Chrome/Konqueror), Opera and the IE9 Platform Preview all offering a decent implementation of the spec, although Mozilla and Webkit still require their respective -moz- and -webkit- prefixes (note Mozilla Firefox 4.0+ no longer requires the -moz- prefix).
In theory, the code for this is straightforward:

#example1 {
box-shadow: 10px 10px 5px #888;
}

But for the moment, as with many other ‘experimental’ CSS3 properties, you’ll need to use the following prefixes to support Mozilla and Webkit:

#example1 {
-moz-box-shadow: 10px 10px 5px #888;
-webkit-box-shadow: 10px 10px 5px #888;
box-shadow: 10px 10px 5px #888;
}

How it Works

The box-shadow property can accept a comma-serparated list of shadows, each defined by 2-4 length values (specifying in order the horizontal offset, vertical offset, optional blur distance and optional spread distance of the shadow), an optional color value and an optional ‘inset‘ keyword (to create an inner shadow, rather than the default outer shadow).

The Syntax:

box-shadow: none | [ , ]*

= inset? && [ {2,4} && ? ]

Examples:

box-shadow: 10px 10px;
box-shadow: 10px 10px 5px #888;
box-shadow: inset 2px 2px 2px 2px black;
box-shadow: 10px 10px #888, -10px -10px #f4f4f4, 0px 0px 5px 5px #cc6600;