ScrollBar background displays as wider than handle

[ECEC]

ScrollBar.vertical: ScrollBar {
            id: scrollBar
            width: 30
            policy: ScrollBar.AlwaysOn
            background: Rectangle {
                color: "#555" //
                radius: 5
            }

            contentItem: Rectangle {
                color: "red"
            }
        }

I'm noticing that the background item in my ScrollBar isn't the same width as my handle, even when I try to set the same width explicitly in scrollBar, background, and contentItem. background seems to be the correct width, but it looks like the handle is narrowing. What's going on here? I'm using Qt 6.6

[ECEC]

@ECEC

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