PostCSS Light Dark Function [][PostCSS]

npm install @csstools/postcss-light-dark-function --save-dev

[PostCSS Light Dark Function] lets you use the light-dark color function in
CSS, following the [CSS Color 5 Specification].

Read more about this feature on mdn:
- define the colors for light and dark with light-dark()
- define which elements support light and/or dark with color-scheme

With both features combined you can mix and match color schemes in a single document, while also respecting the user's preferences.

``css
.foo {
color: light-dark(pink, magenta);
}

.bar {
--bar: light-dark(cyan, deepskyblue);
}

/ becomes /

.foo {
--csstools-light-dark-toggle--0: var(--csstools-color-scheme--light) magenta;
color: var(--csstools-light-dark-toggle--0, pink);
color: light-dark(pink, magenta);
}

.bar {
--csstools-light-dark-toggle--1: var(--csstools-color-scheme--light) deepskyblue;
--bar: var(--csstools-light-dark-toggle--1, cyan);
@supports not (color: light-dark(tan, tan)) {

& * {
--csstools-light-dark-toggle--1: var(--csstools-color-scheme--light) deepskyblue;
--bar: var(--csstools-light-dark-toggle--1, cyan);
}
}
}

@supports (color: light-dark(red, red)) {
.bar {
--bar: light-dark(cyan, deepskyblue);
}
}
`

Declare that your document supports both light and dark mode:

`css
:root {
color-scheme: light dark;
}

/ becomes /

:root {
--csstools-color-scheme--light: initial;
color-scheme: light dark;
}@media (prefers-color-scheme: dark) {:root {
--csstools-color-scheme--light: ;
}
}
`

Dynamically alter the supported color scheme for some elements:

`css
:root {
/ Root only supports light mode /
color-scheme: light;
}

.foo {
/ This element and its children only support dark mode /
color-scheme: dark;
}

/ becomes /

:root {
/ Root only supports light mode /
--csstools-color-scheme--light: initial;
color-scheme: light;
}

.foo {
/ This element and its children only support dark mode /
--csstools-color-scheme--light: ;
color-scheme: dark;
}
`

Usage

Add [PostCSS Light Dark Function] to your project:

`bash
npm install postcss @csstools/postcss-light-dark-function --save-dev
`

Use it as a [PostCSS] plugin:

`js
const postcss = require('postcss');
const postcssLightDarkFunction = require('@csstools/postcss-light-dark-function');

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

Options

$3

The preserve option determines whether the original notation
is preserved. By default, it is preserved.

`js
postcssLightDarkFunction({ preserve: false })
`

`css
.foo {
color: light-dark(pink, magenta);
}

.bar {
--bar: light-dark(cyan, deepskyblue);
}

/ becomes /

.foo {
--csstools-light-dark-toggle--0: var(--csstools-color-scheme--light) magenta;
color: var(--csstools-light-dark-toggle--0, pink);
}

.bar {
--csstools-light-dark-toggle--1: var(--csstools-color-scheme--light) deepskyblue;
--bar: var(--csstools-light-dark-toggle--1, cyan);
& * {
--csstools-light-dark-toggle--1: var(--csstools-color-scheme--light) deepskyblue;
--bar: var(--csstools-light-dark-toggle--1, cyan);
}
}
`

$3

The enableProgressiveCustomProperties option determines whether the original notation
is wrapped with @supports when used in Custom Properties. By default, it is enabled.

> [!NOTE]
> We only recommend disabling this when you set preserve to false or if you bring your own fix for Custom Properties.
> See what the plugin does in its README.

`js
postcssLightDarkFunction({ enableProgressiveCustomProperties: false })
``

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

[PostCSS]: https://github.com/postcss/postcss
[PostCSS Light Dark Function]: https://github.com/csstools/postcss-plugins/tree/main/plugins/postcss-light-dark-function
[CSS Color 5 Specification]: https://drafts.csswg.org/css-color-5/#light-dark