CSS Properties and Values API

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

The CSS Properties and Values API — part of the CSS Houdini umbrella of APIs — allows developers to explicitly define their CSS custom properties, allowing for property type checking, default values, and properties that do or do not inherit their value.

Interfaces

CSS.registerProperty

Defines how a browser should parse CSS custom properties. Access this interface through CSS.registerProperty in JavaScript.

@property

Defines how a browser should parse CSS custom properties. Access this interface through @property at-rule in CSS.

Examples

The following will register a CSS custom property named --my-color using CSS.registerProperty in JavaScript. --my-color will use the CSS color syntax, it will have a default value of #c0ffee, and it will not inherit its value:

js
window.CSS.registerProperty({
  name: "--my-color",
  syntax: "<color>",
  inherits: false,
  initialValue: "#c0ffee",
});

The same registration can take place in CSS using the @property at-rule:

css
@property --my-color {
  syntax: "<color>";
  inherits: false;
  initial-value: #c0ffee;
}

Specifications

Specification
CSS Properties and Values API Level 1
# the-css-property-rule-interface
CSS Properties and Values API Level 1
# the-registerproperty-function

Browser compatibility

api.CSSPropertyRule

Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
CSSPropertyRule
inherits
initialValue
name
syntax

api.CSS.registerProperty_static

Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
registerProperty() static method

See also