← Back

Webpacker 6: PostCSS Loaders

Andrew Mason

Andrew Mason

Published Dec 23rd, 2020

In order to process .pcss files with Webpacker 6, you need to add postcss-loader. I am also going to add PostCSS 8 support.

Note: This section builds on the CSS section


yarn add postcss-loader postcss@latest autoprefixer@latest postcss-import@latest

Add PostCSS Config File

touch postcss.config.js
// postcss.config.js

module.exports = {
  plugins: [


You should be able to use the same pack tag that you added for CSS.

Make sure you restart bin/webpack-dev-server after installing new loaders.

Style Loader Example

<%# app/views/layouts/application.html.erb %>

+ <%= stylesheet_packs_with_chunks_tag 'application', media: 'all', 'data-turbolinks-track': 'reload' %>
<%= javascript_packs_with_chunks_tag 'application', 'data-turbolinks-track': 'reload' %>

Extract Example

<%# app/views/layouts/application.html.erb %>

<%= javascript_packs_with_chunks_tag 'application', 'data-turbolinks-track': 'reload' %>
+ <%= stylesheet_pack_tag 'application', media: 'all', 'data-turbolinks-track': 'reload' %>
// app/javascript/packs/application.js

+ import "./application.css"


Note: Make sure you restart the dev server!

Let’s create a new PostCSS file:

mkdir app/javascript/stylesheets
touch app/javascript/stylesheets/base.pcss

Next, add some CSS:

/* app/javascript/stylesheets/base.pcss */

h1 {
  font-size: 2.2em;
  color: #2563eb;

p {
  font-size: 1.2em;

Lastly, update application.css:

/* app/javascript/packs/application.css */

@import "../stylesheets/base.pcss";

Reload your browser and your styles should be applied now, and the Webpacker loader error should be gone.

Thanks for reading! You can discuss this post using one of the links below. Additionally, it would mean a lot if you shared this post with others!

Recent Posts