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                <div id="projection">
  <div class="pro pro--1">pro--1</div>
  <div class="pro pro--2">pro--2</div>
  <div class="pro pro--3">pro--3</div>


                // magic CORE mixin
@mixin  projection($translateZ: 0, $translateX: 0, $translateY: 0, $width: 0, $height: 0, $perspective: $perspective)

  // strip and sanitize units for further calculations
  // units must be "px" for both $translateZ and $perspective
  $unit: unit( $translateZ )
  @if '' != $unit
    $translateZ: $translateZ / ($translateZ * 0 + 1)
    @if 'px' != $unit
      @warn '$translateZ must have "px" as unit!'

  $unit: unit( $perspective )
  @if '' != $unit
    $perspective: $perspective / ($perspective * 0 + 1)
    @if 'px' != $unit
      @warn '$perspective must have "px" as unit!'

  $unit: 0px // yeah - technically this is no unit
  // calculate scaling factor
  $scale: 1 + ($translateZ * -1) / $perspective

  // sanitize units for translateX, translateY, translateZ
  $translateZ: $translateZ + $unit
  @if unitless( $translateX )
    $translateX: $translateX + $unit
  @if unitless( $translateY )
    $translateY: $translateY + $unit

  // render css "transform: scale() translate(x, y) translateZ()"
  transform: scale( $scale ) translate($translateX, $translateY) translateZ( $translateZ + $unit )


// start CORE
$width: 110% // <=100% works like a charme
$translateZ--1: -3 // "px" will be added in mixin
$translateZ--2: -2
$translateZ--3: -1
$perspective: 1

html, body
  height: 100%
  overflow: hidden
  width: 100%

  transform: translateZ(0)

  perspective: $perspective + 0px
  perspective-origin: center top
  height: 100%
  overflow: auto
  width: 100%
  position: relative

  @include projection()
  height: 100%
  position: absolute
  transform-origin: center top
  transform-style: preserve-3d
  width: 100%
  left: 50%
  margin-left: $width * -.5

  @include projection( $translateZ--1 )
  width: $width

  @include projection( $translateZ--2, 0, 25% )
  width: $width

  @include projection( $translateZ--3, 0, 50% )
  width: $width
// end CORE
// additional styling
  background: #333
  box-shadow: inset 0 0 0 5px orange
  color: orange
  font-size: 4em
  line-height: 1em
  text-align: center

  background: rgba(75,75,75,0.5)
  box-shadow: inset 0 0 0 5px green
  color: green
  line-height: 4em

  background: rgba(75,75,75,0.5)
  box-shadow: inset 0 0 0 5px white
  color: white
  line-height: 7em


Learning 3D transforms in CSS requires a little perspective.