In CSS a box drop shadow can simiulate a 3-d image or dimension.
The code for it is
box-shadow:horizontalOffset verticalOffset [blur] [spread] [color] [inset];
The  are optional values.
Positive number for horizontal offset will place the shadow to the right.
Negative number for horizontal offset will place the shadow to the left of the box.
Positive number for vertical offset will place the shadow below the box.
Negative number for vertical offset will place the shadow above the box.
The blur value affects the edge of the box. The larger the number the blurrier the edge.
Spread value enlarges the drop shadow it can be made larger then the original box. Allows the shadows to be spread out in all directions. It appears as if there is more then one light source instead of just one light source.
The color value can change the color of the drop shadow. It can use either the words for color or the hex code.
The inset word places the shadow inside the box.