How to set ScrollBar indicator width?

[igor_stravinsky]

Qt QuickControls 2, version 5.10...

I've got a vertical ScrollView, and I'm trying to change the width of the vertical ScrollBar's thumb/indicator. I've tried setting the width, and the implicitWidth of the contentItem, but neither seem to change things. Any ideas?

ScrollBar.vertical: ScrollBar{
                policy: ScrollBar.AsNeeded
                anchors.top: parent.top
                anchors.right: parent.right
                anchors.bottom: parent.bottom
                active:pressed
                contentItem: Rectangle{
                    width:4
                    implicitWidth: 4
                    implicitHeight: 100
                    radius: width / 2
                    color: "black"
                }
            }

More specifically, I can change the width by tweaking the implicitWidth property, but I can't seem to get the width smaller than some minimum....