Use bootstrap button classes for two submit buttons

app/views/activities/_form.html.erb

       <%= f.label :reminder_at %>
       <%= f.datetime_field :reminder_at, class: 'form-control' %>
     </div>
-    <%= f.submit %>
+    <%= f.submit class: 'btn btn-primary' %>
   </div>
 <% end %>

app/views/groups/_form.html.erb

       <%= f.label :name %>
       <%= f.text_field :name, class: 'form-control' %>
     </div>
-    <%= f.submit %>
+    <%= f.submit class: 'btn btn-primary' %>
   </div>
 <% end %>