Use CSS3 in applications - Programming in HTML5 with JavaScript and CSS3 - page 255

FIGURE 4-22 The entire shadow of an element displayed by specifying the position to be greater then the
size of the HTML element
Another parameter for the box-shadow is the inset parameter. If omitted, this parameter
creates the shadow on the outside of the box. If inset is specified, the shadow is then created
on the inside of the box. This is demonstrated in the following code:
div{
position: absolute;
left: 50px;top: 50px;
width: 100px;
height: 100px;
border: solid 1px black;
box-shadow: 10px 10px inset;
}
This code produces the output shown in Figure 4-23. The shadow is now displayed on the
inside of the box instead of the outside of the box.
FIGURE 4-23 The use of the inset parameter to place the shadow on the inside of the box