PostCSS Nesting [][PostCSS]

npm install postcss-nesting --save-dev

[PostCSS Nesting] lets you nest style rules inside each other, following the [CSS Nesting specification].

If you want nested rules the same way [Sass] works
you might want to use [PostCSS Nested] instead.

``css
.foo {
color: red;

&:hover {
color: green;
}

> .bar {
color: blue;
}

@media (prefers-color-scheme: dark) {
color: cyan;
}

color: pink;
}

/ becomes /

.foo {
color: red;
}
.foo:hover {
color: green;
}
.foo > .bar {
color: blue;
}
@media (prefers-color-scheme: dark) {
.foo {
color: cyan;
}
}
.foo {

color: pink;
}
`

Usage

Add [PostCSS Nesting] to your project:

`bash
npm install postcss postcss-nesting --save-dev
`

Use it as a [PostCSS] plugin:

`js
const postcss = require('postcss');
const postcssNesting = require('postcss-nesting');

postcss([
postcssNesting(/ pluginOptions /)
]).process(YOUR_CSS /, processOptions /);
`

Options

$3

The CSS nesting feature has gone through several iterations and what is currently implemented in browsers is not the same as what was originally proposed. This plugin dates back to the original proposal and you might have written your CSS expecting this older behavior.

You can pick the older behavior by setting the edition option.
The edition values correspond with rough dates when of a particular version of the specification:
- 2024-02 (default)
- 2021

> [!TIP]
> If you wrote nested rules with @nest you definitely want to set the edition to 2021.
> If you are unsure than you should try to omit the edition option and use the default.

Eventually we will remove support for the older edition, and this plugin option, so it is strongly advised to update your CSS to the latest edition.


`js
postcssNesting({
edition: '2024-02'
})
`

#### 2024-02 (default)

- usage of :is() pseudo-class in the generated CSS is no longer optional. However you can add postcss-is-pseudo-class to transpile further
- at rules are not combined with the and keyword
- @nest is removed from the specification
- declarations and nested rules/at-rules are no longer re-ordered

#### 2021

This version is a continuation of what existed before CSS nesting was implemented in browsers.
It made a few non-invasive changes to keep up with implementations but it is falling behind.

`css
.foo {
color: red;

&:hover {
color: green;
}

> .bar {
color: blue;
}

@media (prefers-color-scheme: dark) {
color: cyan;
}

color: pink;
}

/ becomes /

.foo {
color: red;

color: pink;
}
.foo:hover {
color: green;
}
.foo > .bar {
color: blue;
}
@media (prefers-color-scheme: dark) {
.foo {
color: cyan;
}
}
`

$3

#### Specificity

Before :

`css
#alpha,
.beta {
&:hover {
order: 1;
}
}
`

After without the option :

`js
postcssNesting()
`

`css
:is(#alpha,.beta):hover {
order: 1;
}
`

_.beta:hover has specificity as if .beta where an id selector, matching the specification._

specificity: 1, 1, 0%3Ahover)

After with the option :

`js
postcssNesting({
noIsPseudoSelector: true
})
`

`css
#alpha:hover, .beta:hover {
order: 1;
}
`

_.beta:hover has specificity as if .beta where a class selector, conflicting with the specification._

specificity: 0, 2, 0


#### Complex selectors

Before :

`css
.alpha > .beta {
& + & {
order: 2;
}
}
`

After without the option :

`js
postcssNesting()
`

`css
:is(.alpha > .beta) + :is(.alpha > .beta) {
order: 2;
}
`

After with the option :

`js
postcssNesting({
noIsPseudoSelector: true
})
`

`css
.alpha > .beta + .alpha > .beta {
order: 2;
}
`

_this is a different selector than expected as .beta + .alpha matches .beta followed by .alpha._

_avoid these cases when you disable :is()_

_writing the selector without nesting is advised here_

`css
/ without nesting /
.alpha > .beta + .beta {
order: 2;
}
``

[cli-url]: https://github.com/csstools/postcss-plugins/actions/workflows/test.yml?query=workflow/test
[css-url]: https://cssdb.org/#nesting-rules
[discord]: https://discord.gg/bUadyRwkJS
[npm-url]: https://www.npmjs.com/package/postcss-nesting

[PostCSS]: https://github.com/postcss/postcss
[PostCSS Nesting]: https://github.com/csstools/postcss-plugins/tree/main/plugins/postcss-nesting
[PostCSS Nested]: https://github.com/postcss/postcss-nested
[Sass]: https://sass-lang.com/
[CSS Nesting specification]: https://www.w3.org/TR/css-nesting-1/