=position-list($value1, $value2, $value3, $value4, $value5, $value6)
  $values: $value1 $value2 $value3 $value4 $value5 $value6
  @each $value in $values
    @if optional_nth($value, 2)
      #{nth($value, 1)}: nth($value, 2)
    @else if unitless_number($value)
      z-index: nth($value, 1)
    @else
      position: $value

=absolute($value1: null, $value2: null, $value3: null, $value4: null, $value5: null, $value6: null)
  position: absolute
  +position-list($value1, $value2, $value3, $value4, $value5, $value6)

=fixed($value1: null, $value2: null, $value3: null, $value4: null, $value5: null, $value6: null)
  position: fixed
  +position-list($value1, $value2, $value3, $value4, $value5, $value6)

=relative($value1: null, $value2: null, $value3: null, $value4: null, $value5: null, $value6: null)
  position: relative
  +position-list($value1, $value2, $value3, $value4, $value5, $value6)

=position($value1: null, $value2: null, $value3: null, $value4: null, $value5: null, $value6: null)
  +position-list($value1, $value2, $value3, $value4, $value5, $value6)

=top($position, $z-index: null)
  +relative(top $position, $z-index)
=bottom($position, $z-index: null)
  +relative(bottom $position, $z-index)
=left($position, $z-index: null)
  +relative(left $position, $z-index)
=right($position, $z-index: null)
  +relative(right $position, $z-index)