background of ToolTip template is ignored

// file ToolTip.qml

import QtQuick 2.15
import QtQuick.Templates 2.15 as T

T.ToolTip {
    id: control

    contentItem: Text {
        id: msg
        text: control.text
    }

    background: Rectangle {
        width: msg.implicitWidth
        height: msg.implicitHeight
        color: "red"
    }
}

 // file main.qml

import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15

Window {
    width: 640
    height: 480
    visible: true

    Button {
        anchors.fill: parent
        ToolTip.text: "hello"
        ToolTip.visible: pressed
    }
}