storybook/examples/polymer-cli/src/simple-button.html

<link rel="import" href="../../../node_modules/@polymer/polymer/polymer-element.html">

<dom-module id="simple-button">
  <template>
    <style>
      .simpleButton {
        border: 1px solid black;
        background-color: white;
      }
    </style>
    <button on-click="handleClick" class="simpleButton">
      [[title]]
    </button>
  </template>

  <script>
    class SimpleButton extends Polymer.Element {
      static get is() { return 'simple-button'; }

      static get properties() {
        return {
          title: {
            type: String,
            value: 'Button',
          },
          handleClick: {
            type: Function,
            value: () => {},
          }
        };
      }
    }

    customElements.define(SimpleButton.is, SimpleButton);
  </script>
</dom-module>