media($media)
  if $media == phone
    /* bp-phoneよりも小さい場合のみ */
    @media screen and (max-width: $bp-phone)
      {block}
  else if $media == tablet
    /* bp-phoneよりも大きくbp-tabletよりも小さい場合のみ */
    @media screen and (min-width: $bp-phone) and (max-width: $bp-tablet)
      {block}
  else if $media == pc
    /* bp-tabletよりも大きい場合のみ */
    @media screen and (min-width: $bp-tablet)
      {block}
min-screen($width)
  @media screen and (min-width: $width)
    {block}
max-screen($width)
  @media screen and (max-width: $width)
    {block}