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Prefix every CSS selector with a custom namespace .a => .prefix .a

Table of Contents


$ npm install postcss-prefix-selector

Usage with PostCSS

const prefixer = require('postcss-prefix-selector')

// css to be processed
const css = fs.readFileSync("input.css", "utf8")

const out = postcss().use(prefixer({
  prefix: '.some-selector',
  exclude: ['.c'],

  // Optional transform callback for case-by-case overrides
  transform: function (prefix, selector, prefixedSelector) {
    if (selector === 'body') {
      return 'body' + prefix;
    } else {
      return prefixedSelector;

Using the options above and the CSS below...

body {
  background: red;

.a, .b {
  color: aqua;

.c {
  color: coral;

You will get the following output

body.some-selector {
  background: red;

.some-selector .a, .some-selector .b {
  color: aqua;

.c {
  color: coral;

Usage with webpack

Use it like you'd use any other PostCSS plugin. If you also have autoprefixer in your webpack config then make sure that postcss-prefix-selector is called first. This is needed to avoid running the prefixer twice on both standard selectors and vendor specific ones (ex: @keyframes and @webkit-keyframes).

module: {
  rules: [{
    test: /\.css$/,
    use: [
        loader: require.resolve('postcss-loader'),
        options: {
          postcssOptions: {
            plugins: {
              "postcss-prefix-selector": {
                prefix: '.my-prefix',
                transform(prefix, selector, prefixedSelector, filepath) {
                  if (selector.match(/^(html|body)/)) {
                    return selector.replace(/^([^\s]*)/, `$1 ${prefix}`);
                  if (filepath.match(/node_modules/)) {
                    return selector; // Do not prefix styles imported from node_modules

                  return prefixedSelector;
              autoprefixer: {
                browsers: ['last 4 versions']


Name Type Description
prefix string This string is added before every CSS selector
exclude string[] or RegExp[] It's possible to avoid prefixing some selectors by passing an array of selectors
transform Function In cases where you may want to use the prefix differently for different selectors, it is possible to pass in a custom transform method
ignoreFiles string[] or RegExp[] List of ignored files for processing
includeFiles string[] or RegExp[] List of included files for processing


This project was originally created by @jongleberry and is being maintained by @RadValentin. If you have any questions, feel free to ping the latter.


Please contribute! If you have any questions or bugs, open an issue. Or, open a pull request with a fix.

This project uses Mocha. If you submit a PR, please add appropriate tests and make sure that everything is green for your branch.


MIT © 2015-2021 Jonathan Ong.

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