PostCSS color-mod() Function

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

: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%);
}

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.

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.

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.

Add PostCSS color-mod() Function to your build tool:

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

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

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

postcssColorMod.process(YOUR_CSS);

Add PostCSS to your build tool:

npm install postcss --save-dev

Use PostCSS color-mod() Function as a plugin:

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

postcss([
  postcssColorMod(/* options */)
]).process(YOUR_CSS);

Add Gulp PostCSS to your build tool:

npm install gulp-postcss --save-dev

Use PostCSS color-mod() Function in your Gulpfile:

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

gulp.task('css',
  () => gulp.src('./src/*.css')
  .pipe( postcss([ postcssColorMod(/* options */) ]) )
  .pipe( gulp.dest('.') );

Add Grunt PostCSS to your build tool:

npm install grunt-postcss --save-dev

Use PostCSS color-mod() Function in your Gruntfile:

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

grunt.loadNpmTasks('grunt-postcss');

grunt.initConfig({
  postcss: {
    options: {
      use: [ postcssColorMod(/* options */) ]
    },
    dist: {
      src: '*.css'
    }
  }
});

The stringifier option defines how transformed colors will be produced in CSS. By default, legacy rbg() 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.

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
});

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.