//  PXTOEM
//  Calculate percentage with font-size as context
@function pxtoem($pixels...) {
  $result: '';

  @each $item in $pixels {
    $result: $result + ($item + 0) / $default-font-size + em + ' ';
  }

  @return #{$result};
}

.header-menus {
  padding: pxtoem(0, $grid-gutter-width);
}

padding: 0/pxem 0.75/pxem; (see screenshot)[![enter image description here][2]][2]