Change '--accent-color' in Polymer though whole page under SHADY DOM

Question

I dynamically update the '--accent-color' in all polymer elements with this:

Polymer.updateStyles({'--accent-color': 'red'});

Works fine under Shadow DOM, but in Shady DOM just some of the elements change.

Does anybody knows a way to change the custom style properties defined on

< style is="custom-style">
    :root {
      ...
    }
</style>