Stylus mixin that adds 3d "extrusion" effect to divs

perspective.styl

threed-height = 10px
threed(clr)
    margin-bottom: @margin-bottom + threed-height
    position:relative
    &::after
        content " "
        display block
        border-top: threed-height solid clr;
        border-left: threed-height solid transparent;
        border-right: threed-height solid transparent;
        height: 0
        position: absolute
        bottom -(threed-height)
        left 0
        right 0