$media-xs: 340px
$media-s: 740px
$media-m: 900px
$media-l: 1200px
$media-xl: 1600px

=media($size, $diff: 0, $feature: max-width)

  @if $size == xs
    $size: $media-xs

  @else if $size == s
    $size: $media-s

  @else if $size == m
    $size: $media-m

  @else if $size == l
    $size: $media-l

  @else if $size == xl
    $size: $media-xl

  @media ($feature: $size + $diff)
    @content