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Use CSS @supports to apply styles only when a browser accepts the CSS feature you test. Put a dependable fallback in ordinary CSS first, then add the enhanced styles inside a feature query. A successful query confirms that the browser accepts the tested syntax; it does not guarantee the feature works correctly in every situation.
Check support for a CSS property and value
A declaration query checks a specific property-value pair. Its basic syntax is a parenthesized declaration followed by a block of CSS:
.card {
display: block;
}
@supports (display: grid) {
.card-list {
display: grid;
grid-template-columns: repeat(3, 1fr);
}
}The first rule is the baseline. Browsers that accept display: grid also receive the enhanced layout. Browsers that do not accept it ignore the query block and retain the baseline.
Test the exact value your design needs. A check that a browser accepts a property with one value does not prove it accepts a different, newer value of that property.
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Combine requirements and alternatives
Require every feature with and
Use and when the enhanced style depends on all tested declarations being supported:
@supports (display: grid) and (gap: 1rem) {
.card-list {
display: grid;
gap: 1rem;
}
}Accept any supported option with or
Use or when either declaration is sufficient, such as a standard or prefixed property:
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@supports (text-stroke: 1px) or (-webkit-text-stroke: 1px) {
.outlined-text {
-webkit-text-stroke: 1px;
text-stroke: 1px;
}
}Target browsers that fail a check with not
Use not for a special treatment when a condition is unsupported. Keep the ordinary baseline outside the query where possible, so it remains available to every browser:
@supports not (display: grid) {
.card-list {
/* Styles specifically for browsers without grid support */
}
}Use parentheses to group expressions when combining conditions. For the full syntax and examples, see the MDN reference for the @supports at-rule.
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Check selector syntax instead of a declaration
To test whether a browser accepts a selector, use the selector() form rather than a property-value query:
@supports selector(:has(a)) {
.card:has(a) {
border-color: rebeccapurple;
}
}This checks whether the selector syntax is accepted. The MDN reference also documents feature queries for at-rules and font technology or format.
Choose a fallback that remains useful
- Use a baseline first: write a layout or style that remains usable without the newer feature, then enhance it inside
@supports. - Use a feature query when it changes the fallback decision: browsers generally ignore CSS they do not recognize, so every new declaration does not need a query.
- Use
@supports not (...)selectively: it can add a treatment for browsers missing a feature, but should not replace a sound baseline. - Test real behavior for high-impact features: a positive query means the browser accepts the tested syntax, not that its implementation is bug-free or complete.
MDN describes feature queries as a tool for progressively enhancing a site in its guide to using feature queries.
Check support from JavaScript
JavaScript can check CSS support conditions with CSS.supports(). It is useful when application logic needs to know whether a declaration or condition is accepted; for browser-version support details, consult the API’s dedicated compatibility information.
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- Testing the wrong value: check the exact property-value pair your styles rely on, not merely another value of the same property.
- Checking a selector as if it were a declaration: use
@supports selector(...)for selector syntax. - Expecting a positive result to prove correct rendering: feature queries test syntax support, not every behavioral detail. Verify the outcome in the browsers and devices that matter.
- Putting the only usable style inside the query: move a functional baseline outside it, then place dependent enhancements inside.
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