variable colors with <alpha-value> not working with theme function on plugins

[gsmeira]

I'm trying to create a plugin for Tailwind 3.1.8, but when I use variables on colors with the new syntax - rgb(var(--primary) / <alpha-value>) - the color stop working.

I created an example on https://play.tailwindcss.com/2apCJBfHdC

Removing the / <alpha-value> from the color value make things work again.

I'm doing something wrong?

[Kosai106]

Looks like a PR was opened about this in the past but somehow the behaviour isn't working anymore.
#8652

Related, it would be nice to be able to overwrite the <alpha-value> when using theme(), which I don't believe is possible currently. Looks like that is possible. #9008

[Kosai106]

I hate to be the one doing this but is there any updates on this @thecrypticace?

[thecrypticace]

No worries! Sorry for the late reply. We have been thinking this through some but other things took priority for the v3.2 release.

The reason it doesn't work for plugins like this is two fold:

1. addUtilities doesn't do anything fancy like parsing data types. It's basically to put pure CSS into the stylesheet whenever a utility is used (and it can handle variants ofc)
2. matchUtilities does parse data types and it takes a type option that lists all acceptable "types" for a plugin — as well as a list of values. You get the <alpha-value> behavior for "free" when using it and your type list includes color.

For example, this works today: https://play.tailwindcss.com/1a6LIjNR2S?file=config — Except for the DEFAULT case + opacity modifier which I believe is a bug but I'll have to check on that. However, we're also thinking through what we want to work here.

I think that in an ideal world each plugin would take in the opacity and modify the color itself (or we provide a function to do this for you — not sure though). And we could remove this special case for the color type. We're going to try to dedicate some time soon-ish to figuring out how this should work at a high level for plugin authors to see if:

1. The existing matchUtilities API / workaround is what we want; OR
2. If there's a better, more automatic API that we can design and implement.

[Jakeduncan00]

:root, [data-theme="default"] {
// main
--color-primary-darker: hsl(220, 90%, 36%);
--color-primary-dark: hsl(220, 90%, 46%);
--color-primary: hsl(220, 90%, 56%);
--color-primary-light: hsl(220, 90%, 66%);
--color-primary-lighter: hsl(220, 90%, 76%);
--color-primary-a20: hsla(220, 90%, 56%, 0.2);

--color-accent-darker: hsl(355, 90%, 41%);
--color-accent-dark: hsl(355, 90%, 51%);
--color-accent: hsl(355, 90%, 61%);
--color-accent-light: hsl(355, 90%, 71%);
--color-accent-lighter: hsl(355, 90%, 81%);

// color contrast
--color-bg: hsl(0, 0%, 100%);
--color-bg-a00: hsla(0, 0%, 100%, 0);
--color-contrast-lower: hsl(0, 0%, 95%);
--color-contrast-low: hsl(240, 1%, 83%);
--color-contrast-medium: hsl(240, 1%, 48%);
--color-contrast-high: hsl(240, 4%, 20%);
--color-contrast-higher: hsl(240, 8%, 12%);
--color-contrast-higher-a90: hsla(240, 8%, 12%, 0.9);

// semantic
--color-border: var(--color-contrast-low);
GTA Portal

[Siumauricio]

In the Library that I've created which is RippleUI, I encountered with this same issue, I created a function to apply the opacity and then when some color is called, the function will trigger and if the user specifies a opacity will go there

Definition of variables in this example
https://github.com/Siumauricio/rippleui/blob/main/config/theme/var-theme.ts#L12

The function when a user call some color
https://github.com/Siumauricio/rippleui/blob/main/config/utils/applyOpacityValue.ts#L1

[timkley]

@thecrypticace

hey 👋

I was trying to add a matchUtilities function today to automatically create some utilities from a user-defined set of colors.

I'm using this configuration as explained by you above, but can't seem to get it working like in your example:

plugin(({ matchUtilities, theme }) => {
  matchUtilities(
    {
      foo: (value) => ({ backgroundColor: value }),
    },
    {
      type: ['color'],
      values: theme('colors')
    }
  )
})

The generated CSS looks like this:

background-color: ({ opacityValue =1 })=>oldValue.replace("<alpha-value>", opacityValue) !important;

I tried to rename the property from backgroundColor to color which resulted in the same result.
Trying to call value as a function (value()) seems to kinda work, but results in the following error: TypeError: Cannot read property 'opacityValue' of undefined

I'm using Tailwind CSS v3.2.6.

Can you point me in the right direction?

[karimhossenbux]

It's not working on the class either:
https://play.tailwindcss.com/qLbGj1TFv7

We can't apply opacity when using var(--something)

edit: workaround is to apply alpha with hex color: #00000080 for 50% i.e.

[thecrypticace]

@karimhossenbux The reason you can't apply an opacity to var(--something) is because the colorspace is defined at runtime. What you want is to say bg-[rgba(var(--something))] and not bg-[var(--something)]. Only the 2nd of which can be written in the shorthand bg-[--something].

Until very very recently there has been no way in browsers to augment any arbitrary color and give it an alpha channel.

The only two ways to do this are:

1. Using color-mix() to mix a color with transparent — which multiplies the alpha value.
2. Relative color syntax which can replace a color's alpha channel. You have to make sure to use a color space with a wide gamut in case the source color is also a wide gamut color.

And, unfortunately — at least as of right now — none of those are 100% implemented across all browsers — though I think things have gotten close-ish in just the past 3ish months. Can I Use unfortunately doesn't have up-to-date data at the moment.

[re2005]

Same issue here.

Extending the theme colors won't work.

module.exports = {
    darkMode: 'class',
    content: ['./index.html', './src/**/*.{vue,js,ts,jsx,tsx}'],
    theme: {
        extend: {
            colors: {
                'my-blue': 'rgb(var(--my-color-black) / <alpha-value>)',
            },
        },
    },
    plugins: [],
};