title: QML Rectangle opacity only color
body: <p>I want do set only opacity on my Rectangle. But the text also get transparent.
  How can i only set for the Background.</p>
  
  <pre><code>Rectangle {
                  id: button
                  color: "black"
                  opacity: 0.3
                  width: parent.width
                  height: 35
  
                      Text {
                          anchors.centerIn: parent
                          text: qsTr("text")
                          color: "white"
                          font.pixelSize: 25
                          }
              }
  </code></pre>