CSS content contains unknown CSS properties

This means that the URL in question is a CSS file that contains one or more unknown CSS properties, which will be ignored by browsers.

Why is this important?

It is relatively easy to accidentally make a mistake or typo with a CSS property, which will then be ignored by browsers. These properties add unnecessary bytes to the file size and, although minimal, increase browser resources for rendering.

What does the Hint check?

This Hint will trigger for any internal or external CSS URL which contains unknown CSS properties.

Examples that trigger this Hint:

The Hint would trigger for any style sheet that contains CSS properties which do not match a verified list.

For example, clr isn't a valid property:

a {
 clr: red;
}

Or 'foo' isn't a valid colour:

a {
 color: foo;
}

How do you resolve this issue?

The intent of this Hint is to warn when there are misspellings, so the simplest solution is to go through any unknown properties and fix for typos.