PostCSS and autoprefixing (postcss-loader) with Webpack Encore

PostCSS is a CSS post-processing tool that can transform your CSS in a lot of cool ways, like autoprefixing, linting and more!

First enable it in webpack.config.js:

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// webpack.config.js

  Encore
      // ...
+     .enablePostCssLoader()
  ;

Then restart Encore. When you do, it will give you a command you can run to install any missing dependencies. After running that command and restarting Encore, you're done!

Next, download any plugins you want, like autoprefixer:

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$ npm install autoprefixer --save-dev

Next, create a postcss.config.js file at the root of your project:

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// postcss.config.js
import autoprefixer from 'autoprefixer';

export default {
    plugins: [
        // include whatever plugins you want
        // but make sure you install these via npm!

        // add browserslist config to package.json (see below)
        autoprefixer(),
    ],
};

That's it! The postcss-loader will now be used for all CSS, Sass, etc files. You can also pass options to the postcss-loader by passing a callback:

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// webpack.config.js
+ import path from 'path';

  Encore
      // ...
+     .enablePostCssLoader((options) => {
+         options.postcssOptions = {
+             // the directory where the postcss.config.js file is stored
+             config: path.resolve(import.meta.dirname, 'sub-dir', 'custom.config.js'),
+         };
+     })
  ;

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{
+  "browserslist": [
+    "defaults"
+  ]
  }

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{
+  "browserslist": [
+    "> 0.5%",
+    "last 2 versions",
+    "Firefox ESR",
+    "not dead"
+  ]
  }