first attempt to implement a "jump to top" anchor in the sidebar

doc/utils/sphinx-config/_themes/lammps_theme/layout.html

@@ -137,6 +137,7 @@
           {# the master_doc variable was renamed to root_doc in Sphinx 4 (master_doc still exists in later Sphinx versions) #}
           {%- set _logo_url = logo_url|default(pathto('_static/' + (logo or ""), 1)) %}
           {%- set _root_doc = root_doc|default(master_doc) %}
+          <div id="sidebar-top-target"></div>
           <a href="{{ pathto(_root_doc) }}"{% if not theme_logo_only %} class="icon icon-home"{% endif %}>
             {% if not theme_logo_only %}{{ project }}{% endif %}
             {%- if logo or logo_url %}
@@ -172,6 +173,11 @@
         </div>
         {%- endblock %}
       </div>
+      <div style="padding: 4px;">
+        <center>
+          <a href="#sidebar-top-target"><img src="_static/up.png" alt="(Up)"/> Go to top</a>
+        </center>
+      </div>
     </nav>
 
     <section data-toggle="wy-nav-shift" class="wy-nav-content-wrap">