Border of Group Area

[AmitS]

Hi all,
I am grouping a set of checkbox in a dynamic form,using isGroup(true);,
I am able to group,but i want to remove the border created while grouping.My code is :

DynamicForm roleForm = new DynamicForm();
roleForm.setIsGroup(true);
roleForm.setGroupTitle(menuId);
roleForm.setItems(checkBoxItem);
roleForm.setShowEdges(false);    // Image below is with the use of this code

result is the image attached.Kindly suggest me the functions for this.I checked in google but not able to find the solution.