box-shadow: none;

default

Removes any box-shadow that was applied to the element.

box-shadow: 2px 6px;

You need at least two values:

• the first is the horizontal offset
• the second is the vertical offset

The shadow color will be inherited from the text color.

box-shadow: 2px 6px red;

You can define a color as the last value.

As with color, you can use color names, hexadecimal, rgb, hsl...

box-shadow: 2px 4px 10px red;

The optional third value defines the blur of the shadow.

The color will be diffused across 10px in this example, from opaque to transparent.

box-shadow: 2px 4px 10px 4px red;

The optional fourth value defines the spread of the shadow.

The spread defines how much the shadow should grow: it enhances the shadow.