_z-depth.scss

$_gdm-z-depths: (
  1: (
    top-color: rgba(black, .12),
    top-x-offset: 0,
    top-y-offset: 1,
    top-blur: 1.5,
    bottom-color: rgba(black, .24),
    bottom-x-offset: 0,
    bottom-y-offset: 1,
    bottom-blur: 1
  ),
  2: (
    top-color: rgba(black, .16),
    top-x-offset: 0,
    top-y-offset: 3,
    top-blur: 3,
    bottom-color: rgba(black, .23),
    bottom-x-offset: 0,
    bottom-y-offset: 3,
    bottom-blur: 3
  ),
  3: (
    top-color: rgba(black, .19),
    top-x-offset: 0,
    top-y-offset: 10,
    top-blur: 10, 
    bottom-color: rgba(black, .23),
    bottom-x-offset: 0,
    bottom-y-offset: 6,
    bottom-blur: 3
  ),
  4: (
    top-color: rgba(black, .25),
    top-x-offset: 0,
    top-y-offset: 14,
    top-blur: 14,
    bottom-color: rgba(black, .22),
    bottom-x-offset: 0,
    bottom-y-offset: 10,
    bottom-blur: 5
  ),
  5: (
    top-color: rgba(black, .30),
    top-x-offset: 0,
    top-y-offset: 19,
    top-blur: 19,
    bottom-color: rgba(black, .22),
    bottom-x-offset: 0,
    bottom-y-offset: 15,
    bottom-blur: 6
  )
);

@mixin _gmd-box-shadow($t-top, $t-left, $t-blur, $t-color, $b-top, $b-left, $b-blur, $b-color) {
  -webkit-box-shadow: $t-top+px $t-left+px $t-blur+px $t-color, $b-top+px $b-left+px $b-blur+px $b-color;
  -moz-box-shadow: $t-top+px $t-left+px $t-blur+px $t-color, $b-top+px $b-left+px $b-blur+px $b-color;
  box-shadow: $t-top+px $t-left+px $t-blur+px $t-color, $b-top+px $b-left+px $b-blur+px $b-color;
}

@mixin gmd-z-depth($depth) {
  $settings: map-get($_gdm-z-depths, $depth);
  $t-top: round(map-get($settings, top-x-offset)) * -1;
  $t-left: round(map-get($settings, top-y-offset));
  $t-blur: round(map-get($settings, top-blur));
  $t-color: map-get($settings, top-color);
  $b-top: round(map-get($settings, bottom-x-offset)) * -1;
  $b-left: round(map-get($settings, bottom-y-offset));
  $b-blur: round(map-get($settings, bottom-blur));
  $b-color: map-get($settings, bottom-color);
  
  @include _gmd-box-shadow($t-top, $t-left, $t-blur, $t-color, $b-top, $b-left, $b-blur, $b-color);
}

// TEST

div {
  @include gmd-z-depth(3);
}