=block-size($values)
  @if equal_nth($values, 2)
    +rem('width', nth($values, 1))
    +rem('height', nth($values, 2))
  @else
    +rem('width', nth($values, 1))
    +rem('height', nth($values, 1))

=center-block($values)
  $block-width: optional_nth($values, 1)
  $block-height: optional_nth($values, 2)
  $block-z-index: optional_nth($values, 3)
  +block-size($block-width $block-height)
  +fixed(left 50%, top 50%, $block-z-index)
  +rem('margin-top', $block-height / 2 * -1)
  +rem('margin-left', $block-width / 2 * -1)
  box-sizing: border-box

=horizontal-center-block($values)
  $block-width: optional_nth($values, 1)
  $block-z-index: optional_nth($values, 2)
  +rem('width', $block-width)
  +fixed(left 50%, $block-z-index)
  +rem('margin-left', $block-width / 2 * -1)
  box-sizing: border-box

=square-block($values)
  $square-block-size: optional_nth($values, 1)
  $square-block-height: optional_nth($values, 2)
  $square-block-line-height: optional_nth($values, 3)
  +rem('width', $square-block-size)
  +rem('height', if($square-block-height, $square-block-height, $square-block-size))
  @if $square-block-line-height
    +rem('line-height', $square-block-line-height)
  @else if $square-block-height
    +rem('line-height', $square-block-height)
  @else
    +rem('line-height', $square-block-size)

=over-flow($values)
  $over-flow-x: optional_nth($values, 1)
  $over-flow-y: optional_nth($values, 2)
  @if equal_nth($values, 2)
    over-flow-x: $over-flow-x
    over-flow-y: $over-flow-y
  @else
    over-flow: $over-flow-x

=inline-block($value: null)
  display: inline-block
  vertical-align: $value

=background-size($values)
  +prefixer(background-size, $values, webkit moz spec)

=background-clip($value)
  +prefixer(background-clip, $value, webkit moz spec)

=box-shadow($values...)
  +rem(box-shadow, $values)

=text-shadow($values...)
  +rem(text-shadow, $values)