XAML:
<ContentControl Name="contentControl1" >
<StackPanel>
<StackPanel Name="headerPanel" VerticalAlignment="Top" >
<Grid>
<Label>Header text</Label>
<Button Name="closeButton" Height="20" Width="20" HorizontalAlignment="Right" Click="closeButton_Click">X</Button>
</Grid>
</StackPanel>
<StackPanel Name="contentPanel" VerticalAlignment="Stretch" >
<Label>Hello</Label>
</StackPanel>
</StackPanel>
</ContentControl>
C #:
private void closeButton_Click(object sender, RoutedEventArgs e)
{
contentControl1.Visibility = Visibility.Hidden;
}