How to show the verticalScrollbarUpButton ?

I have creat a scrollView use the code from unity help:
But the scrollview don’t show the verticalScrollbarUpButton.

Are you sure that you have attached the script to a gameObject?

I means is like this

I add image to “Vertical Scrollbar Up Button” and to “Vertical Scrollbar Down Button” (Normal, Hover, Active). I can’t see up/down arrows When i run.