Class for displaying popups with a panel background. Class for displaying popups with a panel background. In some cases it might be simpler to use than [Popup], since it provides a configurable background. If you are making windows, better check [Window]. If any [Control] node is added as a child of this [PopupPanel], it will be stretched to fit the panel's size (similar to how [PanelContainer] works). The background panel style of this [PopupPanel].