Hi. Sorry for the trouble. So just to check, which part are you struggling with at the moment?
Basically it is just a keyframe animation of the sprites for all the different button states. So the first sprite of the animation should be empty, then the second frame is the long thin white sprite, then the slightly taller one, then the blue one.
I don’t know if I explained this very eloquently, but let me know if that helps, otherwise I could send you an example in Unity.