@supports

The @supports CSS at-rule lets you specify declarations that depend on a browser's support for one or more specific CSS features. This is called a feature query. The rule may be placed at the top level of your code or nested inside any other conditional group at-rule.

In JavaScript, @supports can be accessed via the CSS object model interface CSSSupportsRule.

Syntax

The @supports at-rule associates a block of statements with a supports condition. The supports condition consists of one or more name-value pairs combined by conjunctions (and), disjunctions (or), and/or negations (not). Precedence of operators can be defined with parentheses.

Declaration syntax

The most basic supports condition is a simple declaration (a property name followed by a value, separated by a colon). The declaration must be surrounded by parentheses. The following example returns true if the browser's transform-origin property considers 5% 5% valid:

@supports (transform-origin: 5% 5%)

The not operator

The not operator can precede any expression to create a new expression, resulting in the negation of the original one. The following example returns true if the browser's transform-origin property doesn't consider 10em 10em 10em valid:

@supports not (transform-origin: 10em 10em 10em)

As with any operator, the not operator can be applied to a declaration of any complexity. The following examples are both valid:

@supports not (not (transform-origin: 2px))
@supports (display: flexbox) and (not (display: inline-grid))

The and operator

The and operator creates a new expression from the conjunction of two shorter expressions. It returns true only if both of the shorter expressions are also true. The following example returns true if and only if the two shorter expressions are simultaneously true:

@supports (display: table-cell) and (display: list-item)

Multiple conjunctions can be juxtaposed without the need of more parentheses. The following are both equivalent:

@supports (display: table-cell) and (display: list-item) and (display:run-in)
@supports (display: table-cell) and ((display: list-item) and (display:run-in))

The or operator

The or operator creates a new expression from the disjunction of two shorter expressions. It returns true if one or both of the shorter expressions is also true. The following example returns true if at least one of the two shorter expressions is true:

@supports (transform-style: preserve) or (-moz-transform-style: preserve)

Multiple disjunctions can be juxtaposed without the need of more parentheses. The following are both equivalent:

@supports (transform-style: preserve) or (-moz-transform-style: preserve) or 
          (-o-transform-style: preserve) or (-webkit-transform-style: preserve)
@supports (transform-style: preserve-3d) or ((-moz-transform-style: preserve-3d) or
          ((-o-transform-style: preserve-3d) or (-webkit-transform-style: preserve-3d)))

Formal syntax

@supports <supports-condition> {
  <group-rule-body>
}

Examples

Testing for the support of a given CSS property

@supports (animation-name: test) {
  … /* CSS applied when animations are supported with a prefix */
  @keyframes { /* Other at-rules can be nested inside */
    …
  }
}

Testing for the support of a given CSS property or a prefixed version

@supports ((perspective: 10px) or (-moz-perspective: 10px) or (-webkit-perspective: 10px) or
         (-ms-perspective: 10px) or (-o-perspective: 10px)) {
  … /* CSS applied when 3D transforms, prefixed or not, are supported */
}

Testing for the non-support of a specific CSS property

@supports not ((text-align-last: justify) or (-moz-text-align-last: justify)) {
  … /* CSS to provide fallback alternative for text-align-last: justify */
}

Testing for the support of custom properties

@supports (--foo: green) {
  body {
    color: var(--varName);
  }
}

Specifications

Browser compatibility

[1] Gecko 17 to Gecko 21 supported this feature only if the user enables it by setting the config value layout.css.supports-rule.enabled to true.

See also

• The CSSOM class CSSSupportsRule, and the CSS.supports method that allows the same check to be performed via JavaScript.