Make cursor pointer, update docs, and add heading

_sass/content.scss

@@ -165,6 +165,10 @@
     }
   }
 
+  summary {
+    cursor: pointer;
+  }
+
   h1,
   h2,
   h3,

docs/navigation-structure.md

@@ -236,7 +236,9 @@ To generate a Table of Contents on your docs pages, you can use the `{:toc}` met
 
 This example skips the page name heading (`#`) from the TOC, as well as the heading for the Table of Contents itself (`##`) because it is redundant, followed by the table of contents itself. To get an unordered list, replace  `1. TOC` above by `- TOC`.
 
-The table of contents can be made collapsible by adding HTML markup, as in the following example. The attribute `open` and the styling with `{: .text-delta }` are optional.
+### Collapsible Table of Contents
+
+The Table of Contents can be made collapsible using the `<details>` and `<summary>` elements , as in the following example. The attribute `open` (expands the Table of Contents by default) and the styling with `{: .text-delta }` are optional.
 
 ```markdown
 <details open markdown="block">