3D Box Shadow effect

Question

So I know how to do a basic box shadow with CSS3. You can see that in the top of the graphic below.

The effect I\'m trying to achieve is a 3D box shadow, as shown in

Answer 1

Here's a little implementation, inspired by @Vitorino fernandes, in stylus...

offset = 10
border = 3
.offsetbox
   margin offset
   padding offset
   text-align center
   box-shadow inset 0 0 0 unit(border,px) black
   background white
   display inline-block
   position relative
   &:after,
   &:before
      content ''
      background black
      position absolute
   &:after
      width 100%
      height offset
      transform translatey(100%) skewx(-45deg)
      right (offset/2)
      bottom 0
   &:before
      height 100%
      width offset
      transform: translatex(-100%) skewy(-45deg)
      left 0
      top (offset/2)