changing css and template to better visualize sidebar

doc/source/_static/css/default.css

@@ -47,3 +47,12 @@
 .navigator-container .card li {
   padding: 0.2rem 1rem;
 }
+
+/* A "nice" workaround to let us keep l2 level permanently open
+ * but hide child ul's not underneath current selection.
+ * The only eventually open issue is that this way the whole child tree is 
+ * open including all subtrees.
+ */
+.docs-sidebar-toc li.toctree-l2:not(.current) > ul {
+    display: none;
+}

doc/source/templates/sidebartoc.html

@@ -6,7 +6,7 @@
       {%- if theme_sidebar_mode == 'toc' %}
       {{ toc }}
       {%- elif theme_sidebar_mode == 'toctree' %}
-      {{ toctree(maxdepth=2,includehidden=True, collapse=False) }}
+      {{ toctree(maxdepth=4, includehidden=True, collapse=False, titles_only=True) }}
       {%- endif %}
     </div>
   {%- endif %}