Dependency-free breakpoint mixin

breakpoints.scss

/*============================================================================
  Dependency-free breakpoint mixin
    - http://blog.grayghostvisuals.com/sass/sass-media-query-mixin/
==============================================================================*/
$min: min-width;
$max: max-width;
$small: 480px;
$medium: 768px;
$large: 1200px;

@mixin at-query ($constraint, $viewport1, $viewport2:null) {
  @if $constraint == $min {
    @media screen and ($min: $viewport1) {
      @content;
    }
  } @else if $constraint == $max {
    @media screen and ($max: $viewport1) {
      @content;
    }
  } @else {
    @media screen and ($min: $viewport1) and ($max: $viewport2) {
      @content;
    }
  }
}