Spectrum Web Components Won’t Work in CEP

I'm having issues getting Spectrum Web Components to work in a CEP Panel.

As of now, I'm only able to get it to work using the script tag method below. When I try to build a bundle of the node module locally using webpack, it shows correctly in my IDEs HTML preview, but none of the elements load in the CEP panel.

Anyone have any ideas on why this would be?

<script src="https://jspm.dev/@spectrum-web-components/bundle/elements.js" type="module" ></script>