=xs
  @media screen and (max-width: 767px)
    @content

=sm
  @media screen and (min-width: 768px)
    @content

=md
  @media screen and (min-width: 992px)
    @content

=lg
  @media screen and (min-width: 1200px)
    @content

=media($size)
  @media screen and (min-width: $size)
    @content