title: Make QWidget transparent
body: <p>I have a <code>QWidget</code>-based overlay widget which should paint some text and take place over the central widget of my application. The problem is that I can't set background of overlay widget to be transparent. What I already tried:</p>
  
  <ol>
  <li><code>setPalette(Qt::transparent);</code></li>
  <li><code>setAttribute( Qt::WA_TranslucentBackground, true );</code></li>
  <li><code>setAttribute( Qt::WA_OpaquePaintEvent, true );</code></li>
  <li><code>setAutoFillBackground(false);</code></li>
  <li><code>setStyleSheet("QWidget{background-color: transparent;}");</code></li>
  <li><code>setAttribute(Qt::WA_NoSystemBackground);</code></li>
  </ol>