qml中，怎么给Rectangle设置鼠标移入变色，移除恢复？

qml中，怎么给Rectangle设置鼠标移入变色，移除恢复？
Button怎么去掉边框？ Button怎么改变背景色？

import QtQuick 2.4
import QtQuick.Controls 1.3
import QtQuick.Controls.Styles 1.3
import QtQuick.Controls.Private 1.0


Rectangle {
    id:root
    width: 800
    height: 480
    color: "green"


    function mouseEnter(flag){ //处理鼠标进入或者移出变色
        child.color = flag? "cyan":"darkGray"
    }

    Rectangle {
        id: child
        anchors.centerIn: parent
        width: 300
        height: 200
        color: "darkGray"
        MouseArea {
            id: mouseId
            anchors.fill: parent
            hoverEnabled: true
            onEntered: { //监听鼠标进入
                mouseEnter(true);
                //console.log("#### Entered #####")
            }
            onExited: { //监听鼠标移出
                 mouseEnter(false);
                 //console.log("#### Exited #####")
            }
        }
    }

     Button{
         id: button
         width: 100
         height: 30
         x: child.x + child.width + 10
         anchors.bottom: child.bottom

         style: ButtonStyle {
             background: Rectangle {
                 border.color: "transparent"//去掉边框
                 color: control.pressed ? "#CD0000":"#CD00CD" //点击更改颜色
             }
         }
     }
}