Ember CLI minifyCSS options

There's a minifyCSS option in Ember CLI. It takes a property of enabled and options like this:

minifyCSS: {
  enabled: true,
  options: {}
}

I can't find much documentation on it. I want to know what are the possible properties inside the options key? I was hoping to set it up to not remove dead codes in my CSS when compiled to production environment for my specific use-case. For example:

.some-class {
  color: #fff;
  color: --var(--primary-color);
}

The problem is, when compiled to production environment, it will remove dead codes on minification thus leaving only this:

.some-class {
  color: --var(--primary-color);
}

So yeah, what are the possible properties inside the options key. Hopefully there's one option in there that could solve my problem.