title: fitsSystemWindows not making the status bar transparent
body: <p>I had an ConstraintLayout and I want to include the Collapsing Toolbar Layout in it. So, I followed this tutorial: <a href="https://antonioleiva.com/collapsing-toolbar-layout/" rel="noreferrer">https://antonioleiva.com/collapsing-toolbar-layout/</a></p>
  
  <p>But, my status bar is not transparent, even after including fitsSystemWindows in almost every component in my XML.</p>
  
  <p>Here's my style, used in the activity</p>
  
  <pre><code>&lt;style name="AppTheme2" parent="Theme.AppCompat.Light.NoActionBar"&gt;
      &lt;!-- Customize your theme here. --&gt;
      &lt;item name="colorPrimary"&gt;@color/colorPrimary&lt;/item&gt;
      &lt;item name="colorPrimaryDark"&gt;@color/colorPrimaryDark&lt;/item&gt;
      &lt;item name="colorAccent"&gt;@color/colorAccent&lt;/item&gt;
  &lt;/style&gt;
  </code></pre>
  
  <p>The XML layout is too big, so I put it on this gist: <a href="https://gist.github.com/guuilp/6e20ff9e00af8b85c858c5e832a17c34" rel="noreferrer">https://gist.github.com/guuilp/6e20ff9e00af8b85c858c5e832a17c34</a></p>
  
  <p>Furthermore, the back button is not being shown too.</p>