PostCSS Gray lets you use the gray() color function in CSS, following the outdated version of CSS Color Module Level 4 specification (05 November 2019).

⚠️ gray() has been removed from Color Module Level 4 specification.

body {
  background-color: gray(100);
  color: gray(0 / 90%);
}

/* becomes */

body {
  background-color: rgb(255,255,255);
  color: rgba(0,0,0,.9);
}

Add PostCSS Gray to your project:

npm install postcss postcss-color-gray --save-dev

Use PostCSS Gray to process your CSS:

import postcssGray from 'postcss-color-gray';

postcssGray.process(YOUR_CSS /*, processOptions, pluginOptions */);

Or use it as a PostCSS plugin:

import postcss from 'postcss';
import postcssGray from 'postcss-color-gray';

postcss([
  postcssGray(/* pluginOptions */)
]).process(YOUR_CSS /*, processOptions */);

PostCSS Gray runs in all Node environments, with special instructions for:

The preserve option determines whether the original gray() function should be preserved or replaced. By default, the gray() function is replaced.

By setting preserve to true, the original gray() function is preserved.

postcssGray({ preserve: true });

body {
  background-color: gray(100);
  color: gray(0 / 90%);
}

/* becomes */

body {
  background-color: gray(100);
  background-color: rgb(255,255,255);
  color: gray(0 / 90%);
  color: rgba(0,0,0,.9);
}