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Use a usable baseline for every visitor, then add CSS enhancements with feature queries. Check compatibility for the exact property, value, or selector you plan to use, and test the result in the browser versions your audience needs. A positive @supports check means the browser accepts the syntax; it does not prove the feature renders or behaves correctly.
Start with a baseline, then enhance
Progressive enhancement avoids making newer CSS a requirement for basic usability. Write the layout and styles that should work without the optional feature first. Put the enhancement in a conditional block so browsers that do not support it retain a functional fallback.
.card {
display: block;
padding: 1rem;
}
@supports (display: grid) {
.card-list {
display: grid;
grid-template-columns: repeat(2, minmax(0, 1fr));
gap: 1rem;
}
}In this pattern, the baseline remains outside the feature query and the grid enhancement applies only when the browser recognizes the tested declaration. For a new value of a familiar property, test the value too: support for a property does not necessarily mean support for every value.
Use the right condition: feature or environment
Feature support: @supports
A CSS feature query tests whether a browser accepts a declaration or selector syntax. You can combine conditions with and or or, negate one with not, and test selector syntax with selector(). See MDN’s @supports reference for syntax and compatibility details.
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@supports (display: grid) and (gap: 1rem) {
.card-list {
display: grid;
gap: 1rem;
}
}
@supports not (display: grid) {
.card-list {
display: block;
}
}
@supports selector(:focus-visible) {
.control:focus-visible {
outline: 2px solid currentColor;
}
}Keep the fallback outside the query when possible; it is easier to see which styles are universal and which are conditional. Use a negative query only when a distinct fallback is genuinely needed.
Environmental conditions: @media
Media queries test the environment, such as viewport characteristics. They do not test whether a CSS feature is supported. Use @media for responsive or environment-dependent changes, and @supports for capability-dependent CSS. MDN explains this distinction in its feature query guide.
Check compatibility for the exact CSS you use
-
Identify the exact declaration, value, or selector on which the design depends. A familiar property with a newer value still needs its own compatibility check.
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Consult the compatibility information for that feature and the browser versions relevant to your audience. Do not infer support for one feature from support for a related feature.
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Decide what the page should do when the feature is absent. If the answer is “nothing useful,” improve the baseline before adding the enhancement.
-
Test the actual rendering in the relevant browsers, especially when the result depends on behavior rather than simple syntax acceptance. MDN’s guidance on supporting older browsers covers compatibility tables and online testing tools.
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Know what feature detection can and cannot tell you
A true @supports condition means the browser considers the tested declaration or selector valid. It cannot establish that the implementation is complete, follows the specification in every case, or is free of bugs. A browser may accept syntax yet render it differently than your design requires. MDN’s feature-query guide describes these limits.
When correctness depends on a particular behavior, verify that behavior in real browser/version combinations. Feature detection is still preferable to routinely targeting browser names: a browser’s name or user-agent string is a poor stand-in for its actual capabilities. In the rare case where behavior differs despite support being present, test and handle the specific implementation behavior rather than building a stylesheet around broad browser labels. See MDN’s guidance on browser detection using the user-agent string.
Troubleshoot cross-browser CSS differences
-
The enhancement never appears. Check that the query tests the exact property-value pair or selector in use, then confirm support for that exact feature in the target browser version.
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The query passes, but the result looks wrong. The query confirms syntax acceptance, not correct behavior. Reproduce the layout in the affected browser and version, then adjust the implementation or provide a behavior-specific fallback.
-
The old browser shows an unusable page. Move essential layout and content styles into the baseline. Keep unsupported enhancements optional.
-
A browser-specific override keeps breaking elsewhere. Replace name-based rules with capability checks where possible, and scope exceptional handling to the behavior that actually differs.
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-
A responsive rule is being used as a support test. Separate the concerns: use
@mediafor environment conditions and@supportsfor CSS capability.
Or skip the browser setup
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