AEM 6.3, CoralUI slider in dialog: Cannot read property 'contains' of null

If I try to add one of the sliders (to my component dialog) documented on this page: https://docs.adobe.com/docs/en/aem/6-3/develop/ref/coral-ui/coralui3/Coral.Slider.html​, I get the following error:

I think It has something to do with me trying to make it work in the template of a CoralUI.Multifield. If I try the following it works:

$wrapper.append("<coral-slider step=\"2\" min=\"10\" max=\"20\" value=\"14\"></coral-slider>");

This does not work:

var rangedSlider = new Coral.RangedSlider();
rangedSlider.set({
    min: 0,
    max: 50,
    step: 2,
    startValue: 10,
    endValue: 20,
    tooltips: true,
    id: 'rangedSlider'
});
multifield.template.content.appendChild(rangedSlider);

I had no issues with other CoralUI components added using the template (for example a 'CoralUI.Select'), all of them are working fine in my dialog. All help is appreciated!