nav

app/assets/stylesheets/application/layout.sass

-.navbar-brand
-    img
-        max-width: 100px
+.navbar
+    margin-bottom: 100px
+    .navbar-brand
+        img
+            max-width: 100px
 
 footer
     margin-top: 100px

app/services/simple_navigation/bootstrap_renderer.rb

+class SimpleNavigation::BootstrapRenderer < SimpleNavigation::Renderer::Base
+  def render(item_container)
+    content = '<ul class="nav">'
+    item_container.items.each do |item|
+      content << make(item)
+    end
+    content << '</ul>'
+    content.html_safe
+  end
+
+  protected
+
+  def make(item)
+    li = "<li class=\"sidebar-item #{ item.html_options[:class] } #{ ' disabled' unless item.url }\">"
+    li += make_a(item)
+    li += make_subnavigation(item) if consider_sub_navigation?(item)
+    li += '</li>'
+    li
+  end
+
+  def make_item(item)
+    li = "<li class=\"nav-item #{ item.html_options[:class] } #{ ' disabled' unless item.url }\">"
+    li += make_a(item)
+    li += make_subnavigation(item) if consider_sub_navigation?(item)
+    li += '</li>'
+    li
+  end
+
+  def make_a(item)
+    icon = item.send(:options)[:icon]
+    a = "<a href=\"#{ item.url }\" class=\"nav-link#{ item.selected? ? '' : ' collapsed' }\""
+    a += " data-bs-target=\"##{ item.key }\" data-bs-toggle=\"collapse\"" if consider_sub_navigation?(item)
+    a += ">"
+    a += "<i class=\"fas fa-#{ icon }\"></i>" if icon
+    a += "<span class=\"align-middle\">#{ item.name }</span></a>"
+    a
+  end
+
+  def make_subnavigation(item)
+    "<ul id=\"#{ item.key }\" class=\"sidebar-dropdown list-unstyled #{ item.selected? ? 'show' : 'collapse' }\">
+      #{ render_sub_navigation_for item }
+    </ul>"
+  end
+end

config/navigation.rb

 SimpleNavigation::Configuration.run do |navigation|
-  # navigation.renderer = ::Appstack::SimpleNavigationRenderer
+  navigation.renderer = ::SimpleNavigation::BootstrapRenderer
   navigation.auto_highlight = true
   navigation.highlight_on_subpath = true
   navigation.selected_class = 'active'