code: function getCriticalFromAtRule(args) {
    var result = {};
    var options = _extends({
      defaultDest: 'critical.css',
      css: _postcss2.default.root()
    }, args);
  
    options.css.walkAtRules('critical', function (atRule) {
      var name = atRule.params ? atRule.params : options.defaultDest;
      // If rule has no nodes, all the nodes of the parent will be critical.
      var rule = atRule;
      if (!atRule.nodes) {
        rule = atRule.root();
      }
      rule.clone().each(function (node) {
        if (node.name !== 'critical') {
          result[name] = result[name] ? result[name].append(node) : _postcss2.default.root().append(node);
        }
      });
    });
    return result;
  }
docs: Get critical CSS from an at-rule.
  
  @param {Object} args Function args. See flow type alias.