src/language-css/utils.js/isPostcssSimpleVarNode
function isPostcssSimpleVarNode(currentNode, nextNode) {
  return (
    currentNode.value === "$$" &&
    currentNode.type === "value-func" &&
    nextNode &&
    nextNode.type === "value-word" &&
    !nextNode.raws.before
  );
}