How to use the csso.minify function in csso

return new Promise((resolve, reject) => {
    if (source.fileContent && !source.content && source.type == 'css') {
      try {
        source.content = source.compress
          ? require('csso').minify(source.fileContent).css
          : source.fileContent;
        // Change tag type
        source.tag = 'style';
      } catch (err) {
        reject(err);
      }
    }
    resolve();
  });
};

await step('3. generate style.css', async () => {
    const csso = require('csso');

    const stylePaths = [];
    stylePaths.push(...(await globAsync(SRC_PATH, 'ui/**/*.css')));
    stylePaths.push(...(await globAsync(SRC_PATH, 'pptr/**/*.css')));
    stylePaths.push(...(await globAsync(SRC_PATH, 'third_party/**/*.css')));
    const styles = stylePaths.map(stylePath => fs.readFileSync(stylePath, 'utf8'));
    const styleContent = '/* THIS FILE IS GENERATED BY build.js */\n\n' + csso.minify(styles.join('\n'), {restructure: false}).css;
    fs.writeFileSync(path.join(DST_PATH, 'style.css'), styleContent, 'utf8');
  });

formatStyles: (styles: string): Promise => {
      return minify(styles).css; // TODO filter out mapbox styles automatically
    },
    extractStyles: true,

protected isMinified(result: any): boolean {
    const r = CSSO.minify(result.body, {restructure: false}).css;
    return r === result.body;
  }
}

async processCss(assetName, asset, assets) {
    let css = asset.source();
    css = await postcss([autoprefixer({browsers: this.options.browsers})]).process(css).css;

    const result = csso.minify(css, Object.assign({filename: assetName}, this.options));
    css = result.css;

    if (this.options.sourceMap) {
      assets.setAsset(`${assetName}.map`, result.map.toString());
      css += `/*# sourceMappingURL=${path.basename(assetName)}.map */`;
    }

    return css;
  }
}

export async function combineCss(cssFiles: string[]) {
  const cssPromises = await cssFiles.map((path: string) => utils.readFile(path));
  const cssContent = await Promise.all(cssPromises);
  const cssCombined = cssContent.join('\n');
  const compressedCss = csso.minify(cssCombined).css;
  return compressedCss;
}

function readCSS(...args) {
  return csso.minify(fs.readFileSync(path.resolve(...args), "utf8")).css;
}

minimize: function(content) {
        return require('csso').minify(content).css;
    },

function applyOptimization(css = '', cb: Function) {
  try {
    const autoprefixed = postcss([autoprefixer]).process(css).css;
    const minified = csso.minify(autoprefixed).css;
    cb(null, minified);
  }
  catch (err) {
    Logger.error('Problem with autoprefixer/csso. Please create an issue https://github.com/bmvantunes/angular-library-builder');
    cb(err);
  }
}