box-shadow

The box-shadow CSS property describes one or more shadow effects as a comma-separated list. It allows casting a drop shadow from the frame of almost any element. If a border-radius is specified on the element with a box shadow, the box shadow takes on the same rounded corners. The z-ordering of multiple box shadows is the same as multiple text shadows (the first specified shadow is on top).

Values

inset
If not specified (default), the shadow is assumed to be a drop shadow (as if the box were raised above the content).
The presence of the inset keyword changes the shadow to one inside the frame (as if the content was depressed inside the box). Inset shadows are drawn inside the border (even transparent ones), above the background, but below content.

These are two values to set the shadow offset. specifies the horizontal distance. Negative values place the shadow to the left of the element. specifies the vertical distance. Negative values place the shadow above the element. See for possible units.
If both values are 0, the shadow is placed behind the element (and may generate a blur effect if and/or is set).

This is a third value. The larger this value, the bigger the blur, so the shadow becomes bigger and lighter. Negative values are not allowed. If not specified, it will be 0 (the shadow’s edge is sharp).

This is a fourth value. Positive values will cause the shadow to expand and grow bigger, negative values will cause the shadow to shrink. If not specified, it will be 0 (the shadow will be the same size as the element).

See values for possible keywords and notations.
If not specified, the color used depends on the browser – it is usually the value of the color property, but note that Safari currently paints a transparent shadow in this case.

<!DOCTYPE html>
<html>
    <head>
        <style>
            div {
                width: 300px;
                height: 100px;
                background-color: yellow;
                box-shadow: 10px 10px 5px #888888;
            }
        </style>
    </head>
    <body>
        <div>
        </div>
    </body>
</html>