Add comments to app.js

app.js

@@ -1,8 +1,10 @@
+// Set expanded value block to a variable
 const valueBlock = document.getElementById("value-expanded");
 
+// Watch for the details element to be toggled
 document.querySelector('.value-block').addEventListener('toggle', function() {
   if (this.open) {
-    // Code to execute when the details are opened
+    // Scroll to contents of value block when it is opened
     valueBlock.scrollIntoView({ behavior: "smooth" });
   }
 });