Generated by SassMeister.com.

input.scss

.overlay {
    @at-root .mobile & {
        color: green;
    }
    @at-root :not(.mobile) & {
        color: red;
    }
}

output.css

.mobile .overlay {
  color: green;
}

:not(.mobile) .overlay {
  color: red;
}

settings.json

{
  "sass": {
    "compiler": "dart-sass/1.26.11",
    "extensions": {},
    "syntax": "SCSS",
    "outputStyle": "expanded"
  },
  "autoprefixer": false
}