Remove unused css from index.html

gulpfile.js

////////////////////////////////
          //Setup//
////////////////////////////////

// Plugins
var gulp = require('gulp'),
    pjson = require('./package.json'),
    uncss = require('postcss-uncss'),
    comments = require('postcss-discard-comments'),
    cssnext = require('postcss-cssnext'),
    assets = require('postcss-assets'),
    cssnano = require('cssnano'),
    autoprefixer = require('autoprefixer'),
    concat = require('gulp-concat'),
    postcss = require('gulp-postcss'),
    rename = require('gulp-rename')

// Create bundle.min.css file
gulp.task('bundleCss', function() {
  var plugins = [
    uncss({
      html: 'index.html',
      report: true,
    }),
    comments({removeAll: true}),
    cssnext,
    assets,
    cssnano,
    autoprefixer({browsers: ['> 1%'], cascade: false}),
  ];  
  return gulp.src('./css/**/*.css')
    .pipe(concat('bundle.css'))
    .pipe(postcss(plugins))
    .pipe(rename({ suffix: '.min' }))
    .pipe(gulp.dest('./css'));
});

package.json

{
  "name": "",
  "scripts": {
    "gulp": "gulp"
  },
  "devDependencies": {
    "autoprefixer": "^8.4.1",
    "cssnano": "^3.10.0",
    "gulp": "^4.0.0",
    "gulp-postcss": "^7.0.1",
    "gulp-concat": "^2.5.2",
    "gulp-rename": "^1.2.0",
    "postcss-assets": "^5.0.0",
    "postcss-cssnext": "^3.1.0",
    "postcss-discard-comments": "^2.0.4",
    "postcss-uncss": "^0.16.1",
    "uncss": "^0.16.2"
  },
  "dependencies": {}
}