sass-site/source/assets/sass/_breakpoints.scss

$sl-breakpoint--small: 480px !default;
$sl-breakpoint--medium: 640px !default;
$sl-breakpoint--large: 960px !default;
$sl-breakpoint--x-large: 1280px !default;
$sl-breakpoints: (
  // for mixins to span across breakpoints and without one
  none: 0,
  small: $sl-breakpoint--small,
  medium: $sl-breakpoint--medium,
  large: $sl-breakpoint--large,
  x-large: $sl-breakpoint--x-large
);

@mixin sl-breakpoint($breakpoint) {
  @media only screen and (min-width: #{sl-px-to-em($breakpoint)}) {
    @content;
  }
}

@mixin sl-breakpoint-max($breakpoint) {
  @media only screen and (max-width: #{sl-px-to-em($breakpoint)}) {
    @content;
  }
}

@mixin sl-breakpoint--small {
  @include sl-breakpoint($sl-breakpoint--small) {
    @content;
  }
}

@mixin sl-breakpoint--small-max {
  @include sl-breakpoint-max($sl-breakpoint--small) {
    @content;
  }
}

@mixin sl-breakpoint--medium {
  @include sl-breakpoint($sl-breakpoint--medium) {
    @content;
  }
}

@mixin sl-breakpoint--medium-max {
  @include sl-breakpoint-max($sl-breakpoint--medium) {
    @content;
  }
}

@mixin sl-breakpoint--large {
  @include sl-breakpoint($sl-breakpoint--large) {
    @content;
  }
}

@mixin sl-breakpoint--large-max {
  @include sl-breakpoint-max($sl-breakpoint--large) {
    @content;
  }
}

@mixin sl-breakpoint--x-large {
  @include sl-breakpoint($sl-breakpoint--x-large) {
    @content;
  }
}

@mixin sl-breakpoint--x-large-max {
  @include sl-breakpoint-max($sl-breakpoint--x-large) {
    @content;
  }
}

@mixin sl-breakpoint-set($breakpoint, $size) {
  @if $breakpoint == none {
    @content;
  } @else {
    @include sl-breakpoint($size) {
      @content;
    }
  }
}