PostCSS plugin throws a error on any warning from previous PostCSS plugins.

Step 1: Install plugin:

npm install --save-dev postcss postcss-fail-on-warn

Step 2: Check you project for existed PostCSS config: postcss.config.js in the project root, "postcss" section in package.json or postcss in bundle config.

If you do not use PostCSS, add it according to official docs and set this plugin in settings.

Step 3: Add the plugin to plugins list:

module.exports = {
  plugins: [
    require('autoprefixer'),
+   require('postcss-fail-on-warn')
  ]
}