title: Styling a GroupBox
body: <p>I'm trying to create a GroupBox design like this.</p>
  
  <p><img src="https://i.stack.imgur.com/A3BpQ.png" alt="enter image description here"></p>
  
  <p>I have looked at the <code>GroupBox.HeaderTemplate</code></p>
  
  <p>but I'm having problems creating the blue background color, with a width of 100%.
  The same goes for the border.</p>
  
  <p>My code so far</p>
  
  <pre><code>&lt;GroupBox.HeaderTemplate&gt;
                  &lt;DataTemplate&gt;
                      &lt;Grid&gt;
                          &lt;Grid.ColumnDefinitions&gt;
                              &lt;ColumnDefinition Width="*"/&gt;
                          &lt;/Grid.ColumnDefinitions&gt;
                          &lt;Label Content="{Binding}" HorizontalAlignment="Stretch" Background="#25A0DA" Grid.Column="0" Height="20" Padding="5,0,0,0" Margin="1" Foreground="White"/&gt;
                      &lt;/Grid&gt;
                  &lt;/DataTemplate&gt;
              &lt;/GroupBox.HeaderTemplate&gt;
  </code></pre>
  
  <p>And this is what it looks like right now.</p>
  
  <p><img src="https://i.stack.imgur.com/5phYB.png" alt="enter image description here"></p>