Install

npm install postcss-apply

yarn add postcss-apply

postcss-apply

PostCSS plugin enabling custom property sets references

Refer to postcss-custom-properties for DOMless limitations.

Web Platform status

Spec (editor's draft): https://tabatkins.github.io/specs/css-apply-rule
Browser support: https://www.chromestatus.com/feature/5753701012602880

:warning: The @apply rule and custom property sets most likely won't get any more support from browser vendors as the spec is yet considered deprecated and alternative solutions are being discussed.
Refer to following links for more infos:

https://discourse.wicg.io/t/needed-new-champion-for-css-apply-rule/2012
https://github.com/w3c/webcomponents/issues/300#issuecomment-276210974
http://www.xanthir.com/b4o00
https://github.com/w3c/csswg-drafts/issues/1047

Installation

npm install postcss-apply --save-dev

Usage

 const fs = require('fs');
const postcss = require('postcss');
const apply = require('postcss-apply');

const input = fs.readFileSync('input.css', 'utf8');

postcss()
  .use(apply)
  .process(input)
  .then((result) => {
    fs.writeFileSync('output.css', result.css);
  });

Examples

In CSS declared sets

 /* input */

:root {
  --toolbar-theme: {
    background-color: rebeccapurple;
    color: white;
    border: 1px solid green;
  };
}

.Toolbar {
  @apply --toolbar-theme;
}

 /* output */

.Toolbar {
  background-color: rebeccapurple;
  color: white;
  border: 1px solid green;
}

In JS declared sets

 const themes = {
  /* Set names won't be transformed, just `--` will be prepended. */
  'toolbar-theme': {
    /* Declaration properties can either be camel or kebab case. */
    backgroundColor: 'rebeccapurple',
    color: 'white',
    border: '1px solid green',
  },
};

[...]
postcss().use(apply({ sets: themes }))
[...]

 /* input */

.Toolbar {
  @apply --toolbar-theme;
}

 /* output */

.Toolbar {
  background-color: rebeccapurple;
  color: white;
  border: 1px solid green;
}

options

`preserve`

type: Boolean
default: false
Allows for keeping resolved declarations and @apply rules alongside.

`sets`

type: { [customPropertyName: string]: Object | string }
default: {}
Allows you to pass an object or string of custom property sets for :root.
These definitions will be prepended, in such overridden by the one declared in CSS if they share the same name.
The keys are automatically prefixed with the CSS -- to make it easier to share sets in your codebase.