change border.width in button

hi.

i have this qml button. how can i change border.width in c++ code?

Code:

---

import QtQuick 1.1
 
Rectangle {
    id: button
    width: 150
    height: 40
    radius: 10
    gradient: Gradient {
        GradientStop {
            position: 0.41
            color: "#008000"
        }
 
        GradientStop {
            position: 1
            color: "#394f2f"
        }
    }
    clip: true
    smooth: true
    border.color: "red"
    border.width: 0
 
    scale: 1
    rotation: 0
 
    signal qmlClicked(string msg)
    signal clicked()
 
    Text {
        id: name
        x: 77
        y: 27
        text: qsTr("Name")
        font.pointSize: 10
        anchors.verticalCenterOffset: 9
        anchors.horizontalCenterOffset: 26
        style: Text.Sunken
        verticalAlignment: Text.AlignVCenter
        horizontalAlignment: Text.AlignHCenter
        anchors.centerIn: parent; color: "white"
    }
}

---

i can change text, and other things but no border.width