Bubble Shooter Kit Re-skinning guide
How can I customize the game's popups?
All the popups in the game are prefabs located in the Resources/Popups folder that are dynamically spawned via script as appropriate during the game and have an associated independent script that contains their specific logic. In order to modify them, you can drag them into the Canvas object of a scene (as a child) and apply your custom changes to them as you normally do with prefabs in Unity.
These are all the popups in the game: