How to use a mixin or SCSS function to set a property to an element if it is inside an element with a certain class?

Question

Sass

Rough idea of ​​what I want to get

@mixin alt{
   // Что написать здесь, чтоб получить результат, описанный далее ?
}

.test{
  background: red;
  @include alt{
    background: green;
  }
}

.test{background: red}
.alt .test{background: green}

Answer 1

https://www.sassmeister.com/gist/02a5a21b685de4e02...
Anton Litvinenko

@mixin alt {
    .alt & {
      @content;
    }
}

.test{
  background: red;
  @include alt{
    background: green;
  }
}

It?