<===> input.scss

%bam { bam: null; }

@mixin bar() {
   bar: null;
}

@mixin baz() {
   baz: null !important;
}

foo {
  foo: null;
}

bar {
  @include bar;
}

baz {
  @include baz;
}

bam {
  @extend %bam;
}

<===> output.css
bam {
  bam: null;
}

foo {
  foo: null;
}

bar {
  bar: null;
}

baz {
  baz: null !important;
}

<===> output-dart-sass.css
baz {
  baz: !important;
}