Bootstrap Media Query helper

body {
  &:after {
    position: fixed;
    bottom: 0;
    right: 0;
    content: 'xs (- 768px)';
    background: #333;
    color: #fff;
    padding: 3px 6px;
    @include MQ(S) {
      content: 'sm (769px - 992px)';
     }
    @include MQ(M) {
      content: 'md (992px - 1200px)';
    }
    @include MQ(L) {
      content: 'lg (1200px +)'
    }
  }
}