I have a container that I want to put a shape in, and I want it to stretch the full length of the container and be pressed to the top.

I don’t understand why the background colour of the scrollbar doesn’t change. The colour of the slider itself changes, but the background does not. Instead, the background is grainy (you can see on the screenshot). I also noticed that behind the rounded edges of the slider you can see the outlines of the background, which I thought I had set. Now for clarity I put green and noticed that the grainy background also got a slight green tint, I put red background – slight red tint. I suspect that I am editing a parameter that is really responsible for the background, but most likely something is preventing it from working the way I want it to.