title: Material theme doesn't seem to work in QML
body: <p>I have a simple QML with an <code>ApplicationWindow</code>, <code>RowLayout</code> and a bunch of <code>Buttons</code> inside. I have applied the Qt Quick Controls 2 <code>Material</code> theme as per <a href="https://doc-snapshots.qt.io/qt5-5.7/qtquickcontrols2-material.html" rel="noreferrer">the docs</a>, but nothing changed. What's wrong?</p>
  
  <pre><code>import QtQuick 2.7
  import QtQuick.Controls 2.0
  import QtQuick.Controls.Material 2.0
  import QtQuick.Layouts 1.3
  
  ApplicationWindow {
      Material.theme: Material.Dark
      Material.accent: Material.Orange
  
      id: window
      visible: true
  
      RowLayout {
          anchors.horizontalCenter: window.horizontalCenter
          anchors.bottomMargin: 32
  
          Button {
              text: "A"
          }
  
          Button {
              text: "B"
          }
  
          Button {
              text: "C"
          }
      }
  }
  </code></pre>