src/language-css/utils.js/insideAtRuleNode
function insideAtRuleNode(path, atRuleNameOrAtRuleNames) {
  const atRuleNames = [].concat(atRuleNameOrAtRuleNames);
  const atRuleAncestorNode = getAncestorNode(path, "css-atrule");

  return (
    atRuleAncestorNode &&
    atRuleNames.includes(atRuleAncestorNode.name.toLowerCase())
  );
}