.postcssrc.js

module.exports = {
  plugins: [
    require('cssnano')({
      preset: [
        'advanced',
        {
          autoprefixer: { add: true, exclude: false },
          discardComments: { removeAll: true, exclude: false },
          calc: { exclude: true },
          colormin: { exclude: true },
          convertValues: { exclude: true },
          discardDuplicates: true,
          discardEmpty: true,
          discardOverridden: true,
          discardUnused: true,
          mergeIdents: { exclude: true },
          mergeLonghand: { exclude: true },
          mergeRules: true,
          minifyFontValues: { exclude: true },
          minifyGradients: { exclude: true },
          minifyParams: { exclude: true },
          minifySelectors: true,
          normalizeCharset: true,
          normalizeDisplayValues: true,
          normalizePositions: true,
          normalizeRepeatStyle: true,
          normalizeString: { exclude: true },
          normalizeTimingFunctions: { exclude: true },
          normalizeUnicode: { exclude: true },
          normalizeUrl: { exclude: true },
          normalizeWhitespace: { exclude: true },
          orderedValues: { exclude: true },
          reduceIdents: true,
          reduceInitial: true,
          reduceTransforms: true,
          svgo: { exclude: true },
          uniqueSelectors: { exclude: true },
          zindex: { exclude: true }
        }
      ]
    })
  ]
};