title: Style expander header background color in App.xaml
body: <p>I'm trying to create a global style for <code>Expander</code> in <strong>WPF</strong>.</p>
  
  <p>This is what I achieved so far:</p>
  
  <pre><code>&lt;Style TargetType="Expander"&gt;
      &lt;Setter Property="HeaderTemplate"&gt;
          &lt;Setter.Value&gt;
              &lt;DataTemplate&gt;
                  &lt;Border Background="Red"&gt;
                      &lt;ContentControl Content="{Binding}" /&gt;
                  &lt;/Border&gt;
              &lt;/DataTemplate&gt;
          &lt;/Setter.Value&gt;
      &lt;/Setter&gt;
  &lt;/Style&gt;
  </code></pre>
  
  <p>And this is how it looks:</p>
  
  <p><img src="https://i.stack.imgur.com/Px8RI.png" alt="currently looking like this"></p>
  
  <p>Not very satisfying.</p>
  
  <p><strong>Question:</strong> How can I change the background color of the entire <code>Expander</code> header in App.xaml?</p>