$shadow-color-base: rgba(#000, 0.9);
$shadow-offset: 2px;
$shadow-scale: 5px;

@mixin shadow($position: null) {
  @if $position == null {
    box-shadow: 0 (2 * $shadow-offset) (2 * $shadow-scale) $shadow-color-base;
  } @else if $position == bottom {
    box-shadow: 0 $shadow-offset $shadow-scale $shadow-color-base;
  } @else if $position == left {
    box-shadow: (-$shadow-offset) 0 $shadow-scale $shadow-color-base;
  } @else if $position == right {
    box-shadow: $shadow-offset 0 $shadow-scale $shadow-color-base;
  } @else if $position == top-left {
    box-shadow: (-$shadow-offset) (-$shadow-offset) $shadow-scale $shadow-color-base;
  } @else if $position == top-right {
    box-shadow: $shadow-offset (-$shadow-offset) $shadow-scale $shadow-color-base;
  } @else if $position == bottom-left {
    box-shadow: (-$shadow-offset) $shadow-offset $shadow-scale $shadow-color-base;
  } @else if $position == bottom-right {
    box-shadow: $shadow-offset $shadow-offset $shadow-scale $shadow-color-base;
  } @else {
    @warn "position: '#{$position}' is not supported";
  }
}