title: Trouble getting PostCSS to work with Webpack
body: <p>I'm trying to get Webpack to work with PostCSS and am running into trouble. It minifies JavaScript just fine, but doesn't do anything with the CSS. I've tried a variety of configurations based on examples, but can't get it to work. </p>
  
  <p>The main reason I'm doing this is to get PostCSS to make TailwindCSS work on build instead of having to run the CLI command.</p>
  
  <p>Webpack Config:</p>
  
  <pre><code>const path = require('path')
  const MiniCssExtractPlugin = require('mini-css-extract-plugin')
  const UglifyJsPlugin = require("uglifyjs-webpack-plugin");
  const OptimizeCSSAssetsPlugin = require("optimize-css-assets-webpack-plugin");
  
  module.exports = {
    mode: "development",
    entry: {
      app: './src/main.ts',
      vendor: ['./angular']
    },
    output: {
      path: path.join(__dirname, 'src/js'),
      filename: '[name].min.js'
    },
    resolve: {
      extensions: ['.ts', '.js', '.json', '.css']
    },
    module: {
      rules: [
        {
          test: /\.js$/,
          exclude: /node_modules/,
          use: {
            loader: "babel-loader"
          }
        },
        {
          test: /\.tsx?$/,
          loader: "ts-loader"
        },
        {
          test: /\.css$/,
          use: [
            "style-loader",
            MiniCssExtractPlugin.loader,
            "css-loader",
            "postcss-loader"
          ],
        },
      ]
    },
    plugins: [
      new MiniCssExtractPlugin({
        filename: "src/styles.css",
        chunkFilename: "src/css/main.css"
      })
    ]
  }
  </code></pre>
  
  <p>PostCSS Config: </p>
  
  <pre><code>var tailwindcss = require('tailwindcss');
  
  module.exports = {
    plugins: [
        tailwindcss('./tailwind.config.js'),
        require('autoprefixer'),
    ],
  };
  </code></pre>
  
  <p>Package.json</p>
  
  <pre><code>{
  "name": "ateamcoders-app",
  "version": "0.0.0",
  "scripts": {
  "ng": "ng",
  "watch": "webpack --watch --progress --profile",
  "server": "webpack-dev-server --inline --progress --port 8080",
  "start": "npm run server",
  "build": "ng build",
  "test": "ng test",
  "lint": "tslint --force \"src/**/*.ts\"",
  "e2e": "ng e2e"
  },
  "private": true,
  "dependencies": {
  "@angular/animations": "~7.1.0",
  "@angular/common": "~7.1.0",
  "@angular/core": "~7.1.0",
  "@angular/forms": "~7.1.0",
  "@angular/platform-browser": "~7.1.0",
  "@angular/platform-browser-dynamic": "~7.1.0",
  "@angular/router": "~7.1.0",
  "@babel/core": "7.2.0",
  "core-js": "^2.5.4",
  "eslint": "5.10.0",
  "rxjs": "~6.3.3",
  "ts-loader": "5.3.1",
  "tslib": "^1.9.0",
  "zone.js": "~0.8.26"
  },
  "devDependencies": {
  "@angular-devkit/build-angular": "~0.11.0",
  "@angular/cli": "~7.1.2",
  "@angular/compiler": "~7.1.0",
  "@angular/compiler-cli": "~7.1.0",
  "@angular/language-service": "~7.1.0",
  "@types/jasmine": "~2.8.8",
  "@types/jasminewd2": "~2.0.3",
  "@types/node": "~8.9.4",
  "autoprefixer": "9.4.2",
  "babel-loader": "8.0.4",
  "codelyzer": "~4.5.0",
  "cross-env": "5.2.0",
  "css-loader": "2.0.0",
  "enhanced-resolve": "4.1.0",
  "extract-text-webpack-plugin": "3.0.2",
  "html-webpack-plugin": "3.2.0",
  "jasmine-core": "~2.99.1",
  "jasmine-spec-reporter": "~4.2.1",
  "karma": "~3.1.1",
  "karma-chrome-launcher": "~2.2.0",
  "karma-coverage-istanbul-reporter": "~2.0.1",
  "karma-jasmine": "~1.1.2",
  "karma-jasmine-html-reporter": "^0.2.2",
  "mini-css-extract-plugin": "0.5.0",
  "optimize-css-assets-webpack-plugin": "5.0.1",
  "postcss": "7.0.6",
  "postcss-loader": "3.0.0",
  "protractor": "~5.4.0",
  "tailwindcss": "0.7.2",
  "ts-node": "~7.0.0",
  "tslint": "~5.11.0",
  "typescript": "~3.1.6",
  "uglifyjs-webpack-plugin": "2.0.1",
  "webpack": "4.27.1",
  "webpack-cli": "3.1.2",
  "webpack-dev-server": "3.1.10"
  }
  }
  </code></pre>