A CSS post-processor that generates pixel fallbacks for rem units.


A CSS post-processor that generates pixel fallbacks for rem units.
Written with PostCSS.
Add it to your build process with grunt-pixrem.

npm install --save pixrem

Pixrem is a CSS post-processor that, given CSS and a root em value, returns CSS with pixel unit fallbacks or replacements. It's based on browser data so only needed fallbacks will be added. Basically, it's for IE8 or less, and for IE9 & IE10 in the font shorthand property and in pseudo-elements.

'use strict';
var fs = require('fs');
var pixrem = require('pixrem');
var css = fs.readFileSync('main.css', 'utf8');
var processedCss = pixrem.process(css, '200%');
fs.writeFile('main.with-fallbacks.css', processedCss, function (err) {
  if (err) {
    throw err;
  console.log('IE8, you\'re welcome.');

Pixrem takes this:

.sky {
  margin: 2.5rem 2px 3em 100%;
  color: blue;
@media screen and (min-width: 20rem) {
  .leaf {
    margin-bottom: 1.333rem;
    font-size: 1.5rem;

And returns this:

.sky {
  margin: 80px 2px 3em 100%;
  margin: 2.5rem 2px 3em 100%;
  color: blue;
@media screen and (min-width: 20rem) {
  .leaf {
    margin-bottom: 1.333rem;
    font-size: 1.5rem;

Type: String

Some CSS to process.

Type: String | Null
Default: 16px

The root element font size. Can be px, rem, em, %, or unitless pixel value. Pixrem also tries to get the root font-size from CSS (html or :root) and overrides this option. You can use html option to disable it in case you need it.

Type: Object | Null Default: { replace: false, atrules: false, html: true, browsers: 'ie <= 8' }

  • replace replaces rules containing rems instead of adding fallbacks.
  • atrules generates fallback in at-rules too (media-queries)
  • html overrides root font-size from CSS html {} or :root {}
  • browsers sets browser's range you want to target, based on browserslist

Report bugs and feature proposals in the Github issue tracker. Run tests with jasmine-node. In lieu of a formal styleguide, take care to maintain the existing coding style.

1.3.1, Jul 9, 2015

  • Fixed: Replace eachDecl with each and decl.type check in process function

1.3.0, Jul 1, 2015

  • Added: Use browserslist to generate rem fallbacks only when needed

1.2.4, Apr 17, 2015

  • Fixed: generate fallbacks with a value starting with dot

1.2.3, Mar 27, 2015

  • Fix: copy and reduce decl.before, only if defined

1.2.2, Mar 27, 2015

  • Fix root-font size detection

1.2.1, Mar 23, 2015

  • Reduce line-breaks when inserting clone node

1.2.0, Feb 19, 2015

  • Add option html to disable root font-size detection
  • Fix root-font size defined with calc
  • Throw error when root font-size is invalid

1.1.1, Feb 5, 2015:

  • Fix root font-size detection

1.1.0, Jan 25, 2015:

  • PostCSS 4
  • Expose postcss processor

1.0.0, Nov 26, 2014:

  • Generate rem fallbacks only when needed
  • Updated to PostCSS v3.0
  • Get root font-size from CSS

0.1.4, March 6, 2014: Code optimization from AI.
0.1.3, Dec 14, 2013: Fix regex for < 0 values.
0.1.1, 0.1.2, Dec 14, 2013: Documentation improvements.
0.1.0, Dec 14, 2013: Initial release.