fix: query selector needs quotes

Author: IgnaceMaes

addon/modifiers/highlight-active-title.js

@@ -16,7 +16,7 @@ export default modifier(function highlightActiveTitle(element, [toc]) {
   // Track all content sections by id
   toc.forEach((tocItem) => {
     const tocSection = document.querySelector(
-      `section[aria-labelledby=${tocItem.id}]`
+      `section[aria-labelledby="${tocItem.id}"]`
     );
     if (tocSection) {
       observer.observe(tocSection);