how to change scroll box "scroll' images?

Hi, on widgets im using a scroll box and its working fine, but for some reason i am not figuring out how to change that white bar by anything else(doesnt look like even changing colors on all the vertical/horizontal ones seem to do anything)
ideally id be able to change it by an image of mine and if possible even have a different image for the top and down(so i can put arrows).

i wasnt able to find anything online about this so if anyone can offer some input much appreciated.

Old topic, but in case:
Go to your scrollbox in the Designer tab. Right panel, go to “Bar Style” (and not “Style”).
Here you should be able to change a bunch of stuff, like the top image (arrow pointing up for instance), the bottom image (arrow pointing down for instance), the vertical background image, and so on.

Although I would love to know how to get a top and bottom images that stay at the same size no matter how far you can scroll up/down.