use getRootNode API for this reference in click handler (#24)

src/components/card.js

@@ -57,7 +57,7 @@ export default class Card extends HTMLElement {
         <div>
           <h3>${title}</h3>
           <img src="${thumbnail}" alt="${title}" loading="lazy" width="100%">
-          <button onclick="this.parentNode.parentNode.host.selectItem()">View Item Details</button>
+          <button onclick="this.getRootNode().host.selectItem()">View Item Details</button>
         </div>
       `;
       this.attachShadow({ mode: 'open' });