src/language-css/utils/index.js/isDetachedRulesetDeclarationNode
function isDetachedRulesetDeclarationNode(node) {
  const { selector } = node;
  // If a Less file ends up being parsed with the SCSS parser, Less
  // variable declarations will be parsed as atrules with names ending
  // with a colon, so keep the original case then.
  /* istanbul ignore next */
  if (!selector) {
    return false;
  }

  return (
    (typeof selector === "string" && /^@.+:.*$/.test(selector)) ||
    (selector.value && /^@.+:.*$/.test(selector.value))
  );
}