src/language-js/embed/css.js/transformCssDoc
function transformCssDoc(quasisDoc, parentNode, expressionDocs) {
  const isEmpty =
    parentNode.quasis.length === 1 && !parentNode.quasis[0].value.raw.trim();
  if (isEmpty) {
    return "``";
  }

  const newDoc = replacePlaceholders(quasisDoc, expressionDocs);
  /* istanbul ignore if */
  if (!newDoc) {
    throw new Error("Couldn't insert all the expressions");
  }
  return concat(["`", indent(concat([hardline, newDoc])), softline, "`"]);
}