Allows you to use simple block statements to conditionally target +phone, +desktop, and +tablet

screenSizeHelpers.sass

$sizePhone: 603px
$sizeTablet: 1024px

@mixin phone
  @media (max-width: $sizePhone)
    @content

@mixin tablet
  @media (min-width: $sizePhone+1) and (max-width: $sizeTablet)
    @content

@mixin desktop
  @media (min-width: $sizeTablet+1)
    @content

Usage:

h1
  font-size: 50px
  +phone
    font-size: 25px