[css-variables-2] Custom shorthands with `@property`

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
css
Domain
frontend, web-dev

Research direction

Start by reviewing the proposal in this issue and the related CSSWG issue #7273, then examine the surrounding discussion for constraints on custom shorthands, constituent properties, syntax, and keyword behavior. Done means reaching a resolved CSSWG design or specification decision, rather than making a localized code edit.

Written by the indexing model from the issue text.

Description

css-variables-2

Context :

Currently there is no way to reuse small groups of declarations (keys and values) in multiple styles without creating a style rule for them.

.want-to-reuse {
	color: hotpink;
	padding: 15px;
	display: flex;
}

To apply this to multiple components you need to alter your markup.
Or you need to copy/paste the declarations to each style rule.

Mixins are often used to work around this.
I know mixins will never be a thing in native CSS and maybe the same reasons behind that apply to this proposal.

@mixin some-mixin {
	color: hotpink;
	padding: 15px;
	display: flex;
}

selector {
	@include some-mixin;
}

Custom properties also help to some extend because they allow values to be re-used.
Naming conventions help to group sets of values.

:root {
	--some-color: purple;
	--some-padding: 20px;
	--some-display: flex;
	
	--fancy-color: hotpink;
	--fancy-padding: 15px;
	--fancy-display: flex;
}

Proposal :

Can custom shorthands be defined through @property?

  • syntax must match the declared constituent properties
  • keywords like initial work exactly like they work for native shorthands

I included padding in the example but maybe shorthand in shorthands have issues?

@property --some-shorthand {
	syntax: "<color>" "<length>" "<ident>";
	constituent-properties: color padding display;
	values:
		default / purple 20px flex,
		fancy / hotpink 15px flex;
}

.foo {
	--some-shorthand: fancy;
}

Is equivalent to :

.foo {
	color: hotpink;
	padding: 15px;
	display: flex;
}

Set values of constituent properties :

.foo {
	--some-shorthand: green 10px block;
}

This is somewhat related to https://github.com/w3c/csswg-drafts/issues/7273 as it allows similar patterns when styling elements.

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