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  <li>This is originally in light DOM</li>
  <li>This one, too</li>
  <li>Note the CSS style...</li>

<!-- we will use this in our shadow DOM -->
  <!-- This style is only visible for children INSIDE the shadow DOM -->
  <style>li { color: green; }</style>


                li { color: red; } /* only valid outside the shadow DOM */


                const template = document.querySelector('template').content;

class MyList extends HTMLElement {
  connectedCallback() {
    // Note: "this" is the component instance in the DOM tree
    const shadow = this.attachShadow({mode: 'open'})
    const content = template.cloneNode(true)
// grab the <ul> inside our shadow DOM
    const list = shadow.querySelector('ul');     // we query all <li> elements that are inside our component (i.e. the <li> are the light DOM of our component)
   const items = this.querySelectorAll('li')
   // Now we move each of them into the list INSIDE the shadow DOM by appending them to the list...
   items.forEach(li => list.appendChild(li));

window.customElements.define('my-list', MyList);