PostCSS is a popular CSS transpiler with support for a huge ecosystem of plugins.

To use PostCSS with Snowpack: Install @snowpack/plugin-postcss, PostCSS, and your PostCSS plugins, then add this plugin to your Snowpack config.

// snowpack.config.mjs
export default {
+  plugins: ['@snowpack/plugin-postcss'],
};

Lastly, add a postcss.config.js file. By default, @snowpack/plugin-postcss looks for this in the root directory of your project, but you can customize this with the config option. See the plugin README for all available options.

// postcss.config.js
module.exports = {
  plugins: [
    // Replace below with your plugins
    require('cssnano'),
    require('postcss-preset-env'),
  ],
};

Be aware that this plugin will run on all CSS in your project, including any files that compiled to CSS (like .scss Sass files).