Add styling

examples/polyfill_io-replace/public/assets/main.js

@@ -0,0 +1,25 @@
+document.addEventListener('DOMContentLoaded', (event) => {
+  const codeBlock = document.createElement('pre');
+  const codeContent = document.createElement('code');
+  codeContent.className = 'language-html';
+  codeContent.textContent = document.documentElement.outerHTML;
+  codeBlock.appendChild(codeContent);
+  codeBlock.className =
+    'code-block bg-gray-900 text-gray-100 p-4 rounded mt-4 overflow-x-auto text-sm';
+
+  const explanationParagraph = document.createElement('p');
+  explanationParagraph.className = 'mt-4 text-base text-gray-600';
+  explanationParagraph.textContent =
+    'The code block below shows the current HTML document source after the edge function has processed it:';
+
+  const lastParagraph = document.querySelector('body p:last-of-type');
+  if (lastParagraph) {
+    lastParagraph.insertAdjacentElement('afterend', explanationParagraph);
+    explanationParagraph.insertAdjacentElement('afterend', codeBlock);
+  } else {
+    document.body.appendChild(explanationParagraph);
+    document.body.appendChild(codeBlock);
+  }
+
+  Prism.highlightElement(codeContent);
+});