.foo {
  content: 'bar';
}

.bar{
  content: 'baz';
}

.qux {
  content: 'bar';
}

@mixin foo {
  content: 'qux';
}

@mixin bar{
  content: 'qux';
}

.qux {
  content: 'bar';
  @include breakpoint{
    content: bar;
  }
}