src/language-css/utils/index.js/isKeyInValuePairNode
function isKeyInValuePairNode(node, parentNode) {
  if (!isKeyValuePairNode(parentNode)) {
    return false;
  }

  const { groups } = parentNode;
  const index = groups.indexOf(node);

  if (index === -1) {
    return false;
  }

  return isColonNode(groups[index + 1]);
}