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                <!-- Step 1: Create template for the component -->
<template id="vanilla-webcomponent-template">
  <!-- When we insert this into a Shadow DOM, the styles will be scoped -->
    .red {
      color: red;

  Hello, <span class="red">world</span>!

<!-- Step 2: Create custom element class and register it -->
  class VanillaWebcomponent extends HTMLElement {
    constructor() {

      this.attachShadow({ mode: 'open' }); // Creates a shadow DOM root node for the element

      const template = document.getElementById('vanilla-webcomponent-template');
      const templateInstance = template.content.cloneNode(true); // Clones the contents of the template
      this.shadowRoot.appendChild(templateInstance); // Inserts the template contents into the shadow DOM

  customElements.define('vanilla-webcomponent', VanillaWebcomponent);

<!-- Step 3: Render custom component and compare it to non-custom markup -->
<p>Hello, <span class="red">world</span>!</p>