title: How to include additional postCSS plugins (postcss-preset-env) for Angular 7
body: <p>I've recently started implementing CSS custom properties but need to support IE11 - hence the requirement for postcss-preset-env. So far I've discovered Angular's webpack config is not very customizable, but I have since installed custom webpack (<a href="https://www.npmjs.com/package/@angular-builders/custom-webpack" rel="noreferrer">https://www.npmjs.com/package/@angular-builders/custom-webpack</a>).</p>
  
  <p>How do I set up the config file to include and configure the postcss-preset-env plugin to correctly polyfill my CSS custom properties to work in all browsers? I expect any CSS files and also Angular component styles to be compiled with postcss-preset-env. So far I have created a custom-webpack.config.js file with the following:</p>
  
  <pre><code>const postcss = require('postcss-loader');
  const postcssPresetEnv = require('postcss-preset-env');
  
  module.exports = {
    plugins: [
      postcss([
        postcssPresetEnv()
      ]).process()
    ]
  }
  </code></pre>
  
  <p>I've also updated the angular.json build property to reference this file.</p>