Fix collapsible sidebar not working

docs/_static/sidebar.js

@@ -41,9 +41,9 @@ class Sidebar {
 
         icon.addEventListener('click', () => {
           if (icon.classList.contains('expanded')) {
-            collapseSection(icon);
+            this.collapseSection(icon);
           } else {
-            expandSection(icon);
+            this.expandSection(icon);
           }
         })