src/language-css/utils.js/isDetachedRulesetDeclarationNode
function isDetachedRulesetDeclarationNode(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.
  if (!node.selector) {
    return false;
  }

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