Unknown CSS Property
An unknown property error means the CSS property name doesn't exist in the specification. This is usually a typo (e.g., 'colr' instead of 'color'), a vendor-prefixed property used without the prefix, or a made-up property name.
Why It Matters
The browser ignores the entire declaration. Unlike invalid values, unknown properties are easier to catch because the property name itself is wrong. But they can hide behind vendor prefixes and preprocessor variables.
Code Examples
div {
colr: red; /* typo */
font-weigth: bold; /* typo */
background-colour: #fff; /* British spelling */
text-size: 16px; /* not a property */
}div {
color: red;
font-weight: bold;
background-color: #fff;
font-size: 16px;
}How to Fix
- 1Double-check property names. Common typos: colr, font-weigth, backgroud, heigth, widht.
- 2background-colour is not valid CSS. Use background-color (American spelling).
- 3text-size doesn't exist. Use font-size for text sizing.
- 4If using vendor prefixes (-webkit-, -moz-), also include the standard property.
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