GUI: treat fragment as overlay and lose focus onClose

[Supportic]

Hey I've been following this tutorial https://wiki.esoui.com/SimpleNotebookTutorial/part6 and prepared the following code:

local UAN = UniqueAddonName
local window = BoxWindow -- name of the XML TopLevelControl element
local SM = SCENE_MANAGER
 
function UAN.ToogleBox()
  -- just toggles the window
  window:SetHidden(not window:IsHidden())
  -- UI work
  local fragment = ZO_SimpleSceneFragment:New(window)
  local scene = ZO_Scene:New(UAN.name, SM)
  scene:AddFragment(fragment)
  SM:Toggle(UAN.name)
end

The ToogleBox() function is bound to a key and can be closed via a $(parent)BtnClose Button inside the box or via a keybind.

Currently when I toggle the box, everything from the UI will hide except my box and my mouse. Pressing
the key or closing the box via the BtnClose button will hide my mouse and get my UI back.

Goal:
Toggle the box so that the box is acting like a overlay to my current base UI. (without a mouse icon)
By enabling the "mouse icon drag mode" (I don't know the name of this mode ) I should be able to close the box via the button or the keybind. After closing it, the mouse should disappear and my base UI should be brought to the top again.

I hope this is kind of understandable.
Thanks in advance.