@function parent-columns($span)
@if length($span) == 3 @return nth($span, 3) @else if length($span) == 2 @return nth($span, 2) @else @return $columns
@function parent-columns($span)
@if length($span) == 3 @return nth($span, 3) @else if length($span) == 2 @return nth($span, 2) @else @return $columns