[FIX] hide menu until it is correctly specified by the js code.

extensions/odoo_theme/layout.html

@@ -54,7 +54,8 @@
 {% endblock %}
 
 {% block header %}
-    <nav id="o_main_toctree" class="o_side_nav border-end">
+    {# shown when js has properly set all the classes on the toc elements #}
+    <nav id="o_main_toctree" class="o_side_nav border-end" hidden>
         {% include "layout_templates/menu.html" %}
     </nav>
     <header class="o_main_header border-bottom">

extensions/odoo_theme/static/js/menu.js

@@ -1,3 +1,4 @@
+/* global _prepareAccordion */ //see utils.js
 (function ($) {
 
     document.addEventListener('DOMContentLoaded', () => {
@@ -9,6 +10,9 @@
         // Allow to respectively highlight and expand the TOC entries and their related TOC
         // entry list whose page is displayed.
         _flagActiveTocEntriesAndLists();
+
+        // Show hidden menu when the css classes have been properly specified
+        this.navigationMenu.removeAttribute('hidden');
     });
 
     /**

extensions/odoo_theme/static/js/page_toc.js

@@ -1,3 +1,4 @@
+/* global _prepareAccordion */ //see utils.js
 (function ($) {
 
     // Customize the page TOC