Run the following: `npm install && npm run test`. This should be in a directory next to your `cssnano` repo

example.scss

@for $i from 1 through 20000 {
  .foo-#{$i} {
    top: 0;
  }
}

package.json

{
  "name": "playground",
  "type": "commonjs",
  "scripts": {
    "build_sass": "sass example.scss > out.css",
    "minify": "postcss out.css > out_small.css",
    "test": "npm run build_sass && npm run minify"
  },
  "devDependencies": {
    "cssnano": "file:../cssnano/packages/cssnano",
    "postcss": "8.5.6",
    "postcss-cli": "11.0.1",
    "sass": "1.97.3"
  }
}

postcss.config.js

module.exports = {
  plugins: [
    require("cssnano")({
      preset: "default",
    }),
  ],
};