Divider between prod/test in menu

apps/block_scout_web/assets/css/components/_navbar.scss

@@ -161,6 +161,10 @@
 
   &.header {
     font-weight: bold;
+
+    &.division {
+      border-top: 1px solid rgb(183, 185, 184);
+    }
   }
 }
 

apps/block_scout_web/lib/block_scout_web/templates/layout/_topnav.html.eex

@@ -124,7 +124,7 @@
               <%= for %{url: url, title: title} <- main_nets() do %>
                 <a class="dropdown-item" href="<%= url%>"><%= title %></a>
               <% end %>
-              <a class="dropdown-item header">Testnet</a>
+              <a class="dropdown-item header division">Testnet</a>
               <%= for %{url: url, title: title} <- test_nets() do %>
                 <a class="dropdown-item" href="<%= url%>"><%= title %></a>
               <% end %>