How to output multiple css files in Ember app

I am doing an ember build and I have 3 stylesheets that need to compiled into their own stylesheets.

This is how the ember-cli-build.js is by default

const EmberApp = require('ember-cli/lib/broccoli/ember-app');

module.exports = function(defaults) {
  let app = new EmberApp(defaults, {
    'ember-cli-foundation-6-sass': {
      'foundationJs': 'all',
    },
  });

And this is what I have tried but I don't see new files generated. The file paths are correct.

const EmberApp = require('ember-cli/lib/broccoli/ember-app');

module.exports = function(defaults) {
  let app = new EmberApp(defaults, {
    'ember-cli-foundation-6-sass': {
      'foundationJs': 'all',
    },
    css: {
      '/components/icons.data.svg': '/assets/icons.data.svg.css',
      '/components/icons.data.png': '/assets/icons.data.png.css',
      '/components/icons.fallback': '/assets/icons.fallback.css',
    },
  });