Class default

Include the style for the header.

Example:

   import {html, css} from 'lit';
   import {customElement} from 'lit/decorators.js';

   // @ts-ignore
   @customElement('my-panel')
   export default class MyToolPanel extent (window as any).gmfapi.elements.ToolPanelElement {
     static styles = [
       ...(window as any).gmfapi.elements.ToolPanelElement.styles,
       css`...`
     ];

     render(): TemplateResult {
       return html`${this.getTitle(i18next.t('Title'))}
         your template`
     }
   }