Generated by SassMeister.com.

SassMeister-input-HTML.html

<h1><span class="foo">foo<span class="bar">bar</span></span></h1>

SassMeister-input.scss

// ----
// Sass (v3.4.12)
// Compass (v1.0.3)
// ----

@mixin increase-specificity($selector, $specificity: 2) {
  @if $specificity > 1 {
    @include increase-specificity($selector, $specificity - 1) {
      &#{$selector} {
        @content;
      }
    }
  }
  @else {
    #{$selector} {
      @content;
    }
  }
}
 
@include increase-specificity('.foo') {
  color: black;
  
  .bar {
    color: black;
  }
}

.foo {
  color: green;
  
  .bar {
    color: red;
  }
}

SassMeister-output.css

.foo.foo {
  color: black;
}
.foo.foo .bar {
  color: black;
}

.foo {
  color: green;
}
.foo .bar {
  color: red;
}

SassMeister-rendered.html

<h1><span class="foo">foo<span class="bar">bar</span></span></h1>