$breakpoints: (
        'xs':  ( min-width:  480px ),
        'sm':  ( min-width:  768px ),
        'md': ( min-width:  992px ),
        'lg':  ( min-width: 1200px )
) !default;

@mixin respond-to($breakpoint) {
  @if map-has-key($breakpoints, $breakpoint) {
    @media #{inspect(map-get($breakpoints, $breakpoint))} {
      @content;
    }
  }
  @else {
    @warn "Unfortunately, no value could be retrieved from `#{$breakpoint}`. "
        + "Available breakpoints are: #{map-keys($breakpoints)}.";
  }
}