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To give a bit more explanation for why the `color-mod` function 
has been removed (temporarily) from CSS Color Module Level 4.
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PostCSS color-mod() Function PostCSS Logo

NPM Version CSS Standard Status Build Status Support Chat

PostCSS color-mod() Function lets you modify colors using the color-mod() function in CSS, following the outdated version of CSS Color Module Level 4 specification (05 July 2016).

⚠️ color-mod() has been removed from Color Module Level 4 specification. (Here's why)

:root {
  --brand-red:      color-mod(yellow blend(red 50%));
  --brand-red-hsl:  color-mod(yellow blend(red 50% hsl));
  --brand-red-hwb:  color-mod(yellow blend(red 50% hwb));
  --brand-red-dark: color-mod(red blackness(20%));
}

/* becomes */

:root {
  --brand-red:      rgb(255, 127.5, 0);
  --brand-red-hsl:  rgb(255, 127.5, 255);
  --brand-red-hwb:  rgb(255, 127.5, 0);
  --brand-red-dark: rgb(204, 0, 0);
}

/* or, using stringifier(color) { return color.toString() } */

:root {
  --brand-red:      rgb(100% 50% 0% / 100%);
  --brand-red-hsl:  hsl(30 100% 50% / 100%);
  --brand-red-hwb:  hwb(30 0% 0% / 100%);
  --brand-red-dark: hwb(0 0% 20% / 100%);
}

Supported Colors

The color-mod() function accepts rgb(), legacy comma-separated rgb(), rgba(), hsl(), legacy comma-separated hsl(), hsla(), hwb(), and color-mod() colors, as well as 3, 4, 6, and 8 digit hex colors, and named colors without the need for additional plugins.

Implemention details are available in the specification.

Supported Color Adjusters

The color-mod() function accepts red(), green(), blue(), a() / alpha(), rgb(), h() / hue(), s() / saturation(), l() / lightness(), w() / whiteness(), b() / blackness(), tint(), shade(), blend(), blenda(), and contrast() color adjusters.

Implemention details are available in the specification.

Supported Variables

By default, var() variables will be used if their corresponding Custom Properties are found in a :root rule, or if a fallback value is specified.

Usage

Add PostCSS color-mod() Function to your project:

npm install postcss-color-mod-function --save-dev

Use PostCSS color-mod() Function to process your CSS:

const postcssColorMod = require('postcss-color-mod-function');

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

Or use it as a PostCSS plugin:

const postcss = require('postcss');
const postcssColorMod = require('postcss-color-mod-function');

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

PostCSS color-mod() Function runs in all Node environments, with special instructions for:

Node PostCSS CLI Webpack Create React App Gulp Grunt

Options

stringifier

The stringifier option defines how transformed colors will be produced in CSS. By default, legacy rgb() and rgba() colors are produced, but this can be easily updated to support [CSS Color Module Level 4 colors] colors.

import postcssColorMod from 'postcss-color-mod-function';

postcssColorMod({
  stringifier(color) {
    return color.toString(); // use CSS Color Module Level 4 colors (rgb, hsl, hwb)
  }
});

Future major releases of PostCSS color-mod() Function may reverse this functionality so that CSS Color Module Level 4 colors are produced by default.

unresolved

The unresolved option defines how unresolved functions and arguments should be handled. The available options are throw, warn, and ignore. The default option is to throw.

If ignore is used, the color-mod() function will remain unchanged.

import postcssColorMod from 'postcss-color-mod-function';

postcssColorMod({
  unresolved: 'ignore' // ignore unresolved color-mod() functions
});

transformVars

The transformVars option defines whether var() variables used within color-mod() should be transformed into their corresponding Custom Properties available in :root, or their fallback value if it is specified. By default, var() variables will be transformed.

However, because these transformations occur at build time, they cannot be considered accurate. Accurately resolving cascading variables relies on knowledge of the living DOM tree.

importFrom

The importFrom option allows you to import variables from other sources, which might be CSS, JS, and JSON files, and directly passed objects.

postcssColorMod({
  importFrom: 'path/to/file.css' // :root { --brand-dark: blue; --brand-main: var(--brand-dark); }
});
.brand-faded {
  color: color-mod(var(--brand-main) a(50%));
}

/* becomes */

.brand-faded {
  color: rgba(0, 0, 255, .5);
}

Multiple files can be passed into this option, and they will be parsed in the order they were received. JavaScript files, JSON files, and objects will need to namespace custom properties under a customProperties or custom-properties key.

postcssColorMod({
  importFrom: [
    'path/to/file.css',   // :root { --brand-dark: blue; --brand-main: var(--brand-dark); }
    'and/then/this.js',   // module.exports = { customProperties: { '--brand-dark': 'blue', '--brand-main': 'var(--brand-dark)' } }
    'and/then/that.json', // { "custom-properties": { "--brand-dark": "blue", "--brand-main": "var(--brand-dark)" } }
    {
      customProperties: {
        '--brand-dark': 'blue',
        '--brand-main': 'var(--brand-dark)'
      }
    }
  ]
});

Variables may reference other variables, and this plugin will attempt to resolve them. If transformVars is set to false then importFrom will not be used.

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Modify colors using the color-mod() function in CSS

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