.foo {
  content: $content;
  margin: $margin;

  &__element {
    margin: $margin;
  }
}

@mixin blue() {
  margin: $margin;
}

.bar {
  content: ' ';
  margin: 0;

  &__element {
    margin: 0;
  }
}

@mixin red() {
  margin: 0;
}