PostCSS Custom Media 
PostCSS Custom Media lets you use Custom Media Queries in CSS, following the CSS Media Queries specification.
@custom-media --small-viewport (max-width: 30em);
@media (--small-viewport) {
/* styles for small viewport */
}
/* becomes */
@media (max-width: 30em) {
/* styles for small viewport */
}
Usage
Add PostCSS Custom Media to your project:
npm install postcss-custom-media --save-dev
Use PostCSS Custom Media to process your CSS:
const postcssCustomMedia = require('postcss-custom-media');
.process(YOUR_CSS /*, processOptions, pluginOptions */); postcssCustomMedia
Or use it as a PostCSS plugin:
const postcss = require('postcss');
const postcssCustomMedia = require('postcss-custom-media');
postcss([
postcssCustomMedia(/* pluginOptions */)
.process(YOUR_CSS /*, processOptions */); ])
PostCSS Custom Media runs in all Node environments, with special instructions for:
Node | PostCSS CLI | Webpack | Create React App | Gulp | Grunt |
---|
Options
preserve
The preserve
option determines whether custom media and
atrules using custom media should be preserved in their original
form.
@custom-media --small-viewport (max-width: 30em);
@media (--small-viewport) {
/* styles for small viewport */
}
/* becomes */
@custom-media --small-viewport (max-width: 30em);
@media (max-width: 30em) {
/* styles for small viewport */
}
@media (--small-viewport) {
/* styles for small viewport */
}
importFrom
The importFrom
option specifies sources where custom
media can be imported from, which might be CSS, JS, and JSON files,
functions, and directly passed objects.
postcssCustomMedia({
importFrom: 'path/to/file.css' // => @custom-selector --small-viewport (max-width: 30em);
; })
@media (max-width: 30em) {
/* styles for small viewport */
}
@media (--small-viewport) {
/* styles for small viewport */
}
Multiple sources can be passed into this option, and they will be
parsed in the order they are received. JavaScript files, JSON files,
functions, and objects will need to namespace custom media using the
customMedia
or custom-media
key.
postcssCustomMedia({
importFrom: [
'path/to/file.css',
'and/then/this.js',
'and/then/that.json',
{customMedia: { '--small-viewport': '(max-width: 30em)' }
,
}=> {
() const customMedia = { '--small-viewport': '(max-width: 30em)' };
return { customMedia };
}
]; })
exportTo
The exportTo
option specifies destinations where custom
media can be exported to, which might be CSS, JS, and JSON files,
functions, and directly passed objects.
postcssCustomMedia({
exportTo: 'path/to/file.css' // @custom-media --small-viewport (max-width: 30em);
; })
Multiple destinations can be passed into this option, and they will
be parsed in the order they are received. JavaScript files, JSON files,
and objects will need to namespace custom media using the
customMedia
or custom-media
key.
const cachedObject = { customMedia: {} };
postcssCustomMedia({
exportTo: [
'path/to/file.css', // @custom-media --small-viewport (max-width: 30em);
'and/then/this.js', // module.exports = { customMedia: { '--small-viewport': '(max-width: 30em)' } }
'and/then/this.mjs', // export const customMedia = { '--small-viewport': '(max-width: 30em)' } }
'and/then/that.json', // { "custom-media": { "--small-viewport": "(max-width: 30em)" } }
,
cachedObject=> {
customMedia // { '--small-viewport': '(max-width: 30em)' }
customMedia
}
]; })