如何将DOM元素扩展为一个类(没有jQuery)

// 定义自定义类
class MyElement extends HTMLElement {
  constructor() {
    super();
    this.attachShadow({ mode: 'open' });
  }

  connectedCallback() {
    this.shadowRoot.innerHTML = `
     <style>
        :host {
          display: block;
          background-color: lightblue;
          padding: 10px;
        }
      </style>
      <p>Hello, I'm a custom element!</p>
    `;
  }
}

// 定义自定义元素
customElements.define('my-element', MyElement);

<my-element></my-element>