PostCSS Alpha Function

npm install @csstools/postcss-alpha-function --save-dev

PostCSS Alpha Function lets you use the alpha function in CSS, following the CSS Color specification.

.color {
    color: alpha(from #dddd / calc(alpha / 2));
}

:root {
    --a-color: alpha(from rgb(2 1 0 / var(--a)) / calc(alpha / 2));
}

/* becomes */

.color {
    color: rgb(from #dddd r g b / calc(alpha / 2));
}

:root {
    --a-color: rgb(from rgb(2 1 0 / var(--a)) r g b / calc(alpha / 2));
}

Usage

Add PostCSS Alpha Function to your project:

npm install postcss @csstools/postcss-alpha-function --save-dev

Use it as a PostCSS plugin:

const postcss = require('postcss');
const postcssAlphaFunction = require('@csstools/postcss-alpha-function');

postcss([
    postcssAlphaFunction(/* pluginOptions */)
]).process(YOUR_CSS /*, processOptions */);

Options

preserve

The preserve option determines whether the original notation is preserved. By default, it is not preserved.

postcssAlphaFunction({ preserve: true })

.color {
    color: alpha(from #dddd / calc(alpha / 2));
}

:root {
    --a-color: alpha(from rgb(2 1 0 / var(--a)) / calc(alpha / 2));
}

/* becomes */

.color {
    color: rgb(from #dddd r g b / calc(alpha / 2));
    color: alpha(from #dddd / calc(alpha / 2));
}

:root {
    --a-color: rgb(from rgb(2 1 0 / var(--a)) r g b / calc(alpha / 2));
}

@supports (color: alpha(from red / 1)) and (color: rgb(0 0 0 / 0)) {
:root {
    --a-color: alpha(from rgb(2 1 0 / var(--a)) / calc(alpha / 2));
}
}

enableProgressiveCustomProperties

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.

postcssAlphaFunction({ enableProgressiveCustomProperties: false })

.color {
    color: alpha(from #dddd / calc(alpha / 2));
}

:root {
    --a-color: alpha(from rgb(2 1 0 / var(--a)) / calc(alpha / 2));
}

/* becomes */

.color {
    color: rgb(from #dddd r g b / calc(alpha / 2));
    color: alpha(from #dddd / calc(alpha / 2));
}

:root {
    --a-color: rgb(from rgb(2 1 0 / var(--a)) r g b / calc(alpha / 2));
    --a-color: alpha(from rgb(2 1 0 / var(--a)) / calc(alpha / 2));
}

Custom properties do not fallback to the previous declaration

Copyright : color conversions

This software or document includes material copied from or derived from https://github.com/w3c/csswg-drafts/tree/main/css-color-4. Copyright © 2022 W3C® (MIT, ERCIM, Keio, Beihang).