block3.js

import { LitElement, html, css } from 'lit-element';

export class LeaTab extends LitElement {
  static get styles() {
    return css`/* my stylings */`;
  }

  render() {
    return html`
      <!-- dom as needed -->
      <slot></slot>
    `;
  }
}

customElements.define('lea-tab', LeaTab);