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  <!-- Polyfills only needed for Firefox and Edge. -->
  <script src=""></script>
  <!-- Loads natively on browsers that support Javascript modules like
       Chrome, Safari, Firefox 60, Edge 16. For all others, use a
       module-compatible toolchain like Polymer CLI, WebPack, or Rollup -->
  <script type="module">
    import {PolymerElement, html} from '';

    class MyElement extends PolymerElement {

      static get properties() { return { mood: String }}

      static get template() {
        return html`
          <style> .mood { color: green; } </style>
          Web Components are <span class="mood">[[mood]]</span>!

    customElements.define('my-element', MyElement);
  <my-element mood="awesome"></my-element>