The list of supported CSS @-rules is growing quite large, and it's very easy to miss a typo.
This rule checks each @-rule name to make sure that it is a known CSS @-rule. All vendor-prefixed @-rules are ignored because vendors may add in their own @-rules at any point in time.
@abc { /* Noncompliant: 'abc' isn't a known @-rule */
color: red;
}
@import url("styles.css"); /* Compliant: 'import' is a known @-rule */
@-moz-vendoratrule {} /* Compliant: '-moz-vendoratrule is a vendor @-rule */