discourse/app/assets/stylesheets/common/foundation/spacing.scss

$base-space: 4px;

@function s(
  $sizes: (
    0
  )
) {
  $spaces: ();
  @each $size in $sizes {
    @if ($size == 0) {
      // Strip units if 0
      $size: $size * $base-space;
      $size: $size / ($size * 0 + 1);
    } @else if ($size == auto) {
      $size: auto;
    } @else {
      $size: $size * $base-space;
    }

    $spaces: append($spaces, $size);
  }
  @return $spaces;
}