@font-feature-values CSS at-rule marked as unrecognized.

[Electricz0]

The @font-feature-values at-rule is unrecognized by the CSS validator.

Information about this at-rule can be found here:

https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/At-rules/@font-feature-values

Example CSS code to validate and reproduce the error:

@font-feature-values Fira Code {
    @character-variant {
        alt-a: 1;
        alt-g: 2;
        alt-i-1: 3;
    }
}

Error message:

Error Unrecognized at-rule @font-features-values
From line 1, column 1; to line 1, column 20
@font-feature-values {↩ @c