Box-Shadows:

box-Shadows: (from the left)(from the top)(spread)(color)

box-Shadows: (horizontal offset)(vertical offset)(blur radius "optional")(spread radius "optional")(color)

1

2

3
inset

Box1: box-shadow:2px 2px 6px black;

Box2 inset: box-shadow:2px 2px 6px black inset;

Box3 both:-10px -10px 1px -3px #CDCDCD, 4px 4px 2px -2px black inset;

Syntax
box-shadow: w-shadow h-shadow blur spread color inset;

You can add inset at the end to place the box shadow inside the box but if you want the shadow on the outside then leave out the inset.