PostCSS Design Tokens

npm install @csstools/postcss-design-tokens --save-dev

PostCSS Design Tokens lets you use design tokens in your CSS source files.

{
    "color": {
        "background": {
            "primary": { "value": "#fff" }
        }
    },
    "size": {
        "spacing": {
            "small": { "value": "16px" },
            "medium": { "value": "18px" },
            "medium-alias": { "value": "{size.spacing.medium}" }
        }
    },
    "viewport": {
        "medium": { "value": "35rem" }
    }
}

@design-tokens url('./tokens.json') format('style-dictionary3');

.foo {
    color: design-token('color.background.primary');
    padding-top: design-token('size.spacing.small');
    padding-left: design-token('size.spacing.small' to px);
    padding-bottom: design-token('size.spacing.small' to rem);
}

@media (min-width: design-token('viewport.medium')) {
    .foo {
        padding-bottom: design-token('size.spacing.medium-alias' to rem);
    }
}

/* becomes */

.foo {
    color: #fff;
    padding-top: 16px;
    padding-left: 16px;
    padding-bottom: 1rem;
}

@media (min-width: 35rem) {
    .foo {
        padding-bottom: 1.125rem;
    }
}

Usage

Add PostCSS Design Tokens to your project:

npm install postcss @csstools/postcss-design-tokens --save-dev

Use it as a PostCSS plugin:

const postcss = require('postcss');
const postcssDesignTokens = require('@csstools/postcss-design-tokens');

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

Formats

At this time there is no standardized format for design tokens. Although there is an ongoing effort to create this, we feel it is still too early to adopt this.

For the moment we only support Style Dictionary. Use style-dictionary3 in @design-tokens rules to pick this format.

Options

is

The is option determines which design tokens are used.
This allows you to generate multiple themed stylesheets
by running PostCSS multiple times with different configurations.

By default only @design-tokens without any when('foo') conditions are used.

This plugin itself does not produce multiple outputs, it only provides an API to change the output.

Example usage

For these two token files :

{
    "color": {
        "background": {
            "primary": { "value": "#0ff" }
        }
    }
}

{
    "color": {
        "background": {
            "primary": { "value": "#f0f" }
        }
    }
}

And this CSS :

@design-tokens url('./tokens-brand-1.json') format('style-dictionary3');
@design-tokens url('./tokens-brand-2.json') when('brand-2') format('style-dictionary3');

.foo {
    color: design-token('color.background.primary');
}

You can configure :

No is option.

postcssDesignTokens()

@design-tokens url('./tokens-brand-1.json') format('style-dictionary3');
@design-tokens url('./tokens-brand-2.json') when('brand-2') format('style-dictionary3');

.foo {
    color: design-token('color.background.primary');
}

/* becomes */

.foo {
    color: #0ff;
}

is option set to 'brand-2'.

postcssDesignTokens({ is: ['brand-2'] })

@design-tokens url('./tokens-brand-1.json') format('style-dictionary3');
@design-tokens url('./tokens-brand-2.json') when('brand-2') format('style-dictionary3');

.foo {
    color: design-token('color.background.primary');
}

/* becomes */

.foo {
    color: #f0f;
}

unitsAndValues

The unitsAndValues option allows you to control some aspects of how design values are converted to CSS. rem <-> px for example can only be calculated when we know the root font size.

rootFontSize

defaults to 16

postcssDesignTokens({
    unitsAndValues: {
        rootFontSize: 20,
    },
})

@design-tokens url('./tokens.json') format('style-dictionary3');

.foo {
    color: design-token('color.background.primary');
    padding-top: design-token('size.spacing.small');
    padding-left: design-token('size.spacing.small' to px);
    padding-bottom: design-token('size.spacing.small' to rem);
}

@media (min-width: design-token('viewport.medium')) {
    .foo {
        padding-bottom: design-token('size.spacing.medium-alias' to rem);
    }
}

/* becomes */

.foo {
    color: #fff;
    padding-top: 16px;
    padding-left: 16px;
    padding-bottom: 0.8rem;
}

@media (min-width: 35rem) {
    .foo {
        padding-bottom: 0.9rem;
    }
}

Customize function and at rule names

importAtRuleName

The importAtRuleName option allows you to set a custom alias for @design-tokens.

postcssDesignTokens({ importAtRuleName: 'tokens' })

@tokens url('./tokens.json') format('style-dictionary3');

.foo {
    color: design-token('color.background.primary');
    padding-top: design-token('size.spacing.small');
    padding-left: design-token('size.spacing.small' to px);
    padding-bottom: design-token('size.spacing.small' to rem);
}

/* becomes */

.foo {
    color: #fff;
    padding-top: 16px;
    padding-left: 16px;
    padding-bottom: 1rem;
}

valueFunctionName

The valueFunctionName option allows you to set a custom alias for design-token.

postcssDesignTokens({ valueFunctionName: 'token' })

@design-tokens url('./tokens.json') format('style-dictionary3');

.foo {
    color: token('color.background.primary');
    padding-top: token('size.spacing.small');
    padding-left: token('size.spacing.small' to px);
    padding-bottom: token('size.spacing.small' to rem);
}

/* becomes */

.foo {
    color: #fff;
    padding-top: 16px;
    padding-left: 16px;
    padding-bottom: 1rem;
}

Syntax

PostCSS Design Tokens is non-standard and is not part of any official CSS Specification.

Editor support

This is all very new and we hope that one day design tokens will become first class citizens in editors and other tools. Until then we will do our best to provide extensions. These will have rough edges but should illustrate were we want to go.

@design-tokens rule

The @design-tokens rule is used to import design tokens from a JSON file into your CSS.

@design-tokens url('./tokens.json') format('style-dictionary3');

@design-tokens url('./tokens.json') format('style-dictionary3');
@design-tokens url('./tokens-dark-mode.json') format('style-dictionary3') when('dark');

You can also import tokens from an npm package:

@design-tokens url('node_modules:my-npm-package/tokens.json') format('style-dictionary3');
@design-tokens url('node_modules:my-npm-package/tokens-dark-mode.json') format('style-dictionary3') when('dark');

@design-tokens [ <url> | <string> ]
               [ when(<theme-condition>*) ]?
               format(<format-name>);

<theme-condition> = <string>

<format-name> = [ 'style-dictionary3' ]

All @design-tokens rules in a document are evaluated in order of appearance. If a token with the same path and name already exists it will be overridden.

All @design-tokens rules are evaluated before any design-token() functions.

@design-tokens rules can be conditional through when conditions. Multiple values can be specified in when.
Multiple conditions always have an AND relationship.

/* only evaluated when tooling receives 'blue' and 'muted' as arguments */
@design-tokens url('./tokens.json') format('style-dictionary3') when('blue' 'muted');

@design-tokens rules can never be made conditional through @supports, @media or other conditional rules.

@media (min-width: 500px) {
  @design-tokens url('./tokens.json') format('style-dictionary3'); /* always evaluated */
}

Any form of nesting is meaningless, @design-tokens will always be evaluated as if they were declared at the top level.

design-token() function

The design-token() function takes a token path and returns the token value.

.foo {
    color: design-token('color.background.primary');
}

design-token() = design-token( <token-path> [ to <unit> ]? )

<token-path> = <string>
<unit> = [ px | rem | ... ]

The plugin can convert px to rem and rem to px via the unitsandvalues plugin options. When a design token is unit-less any unit can be assigned with to.

Stylelint

Stylelint is able to check for unknown property values. Setting the correct configuration for this rule makes it possible to check even non-standard syntax.

    // Disallow unknown values for properties within declarations.
    'declaration-property-value-no-unknown': [
        true,
        {
            propertiesSyntax: {
                color: '| <design-token()>',
                // ... more properties ...
            },
            typesSyntax: {
                '<design-token()>': 'design-token( <string> [ to <ident> ]? )',
            },
        },
    ],

Further reading

• Why we think PostCSS Design Tokens is needed
• About Design Tokens (Adobe Spectrum)