npm install @csstools/postcss-alpha-function --save-devPostCSS 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));
}Add PostCSS Alpha Function to your project:
npm install postcss @csstools/postcss-alpha-function --save-devUse it as a PostCSS plugin:
const postcss = require('postcss');
const postcssAlphaFunction = require('@csstools/postcss-alpha-function');
postcss([
postcssAlphaFunction(/* pluginOptions */)
]).process(YOUR_CSS /*, processOptions */);PostCSS Alpha Function runs in all Node environments, with special instructions for:
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));
}
}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
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).
