Question how to call the event of window1 to window 2 in WPF

[SAE]

The Idea is that when I start the application 2 windows pop up. On mainwindow I have button and on window1 I have label and when I press the button the label color should change.

This is what Far have tried so far but it didn't work. What am I doing wrong ? and how to make it work ?
Note: in the wpf app am not using Model View ViewModel.

public partial class MainWindow : Window

{
public MainWindow()
{
InitializeComponent();


}

private void btnFirstWindow_Click(object sender, RoutedEventArgs e)
{
Window1 sWindow = new Window1(btnFirstWindow);
sWindow.Show();

}
}

Mainwindow XAML

Title="MainWindow" Height="450" Width="800">

<Grid>

<Button x:Name="btnFirstWindow" Content="Button" HorizontalAlignment="Left" Height="140" Margin="492,77,0,0" VerticalAlignment="Top" Width="151" Click="btnFirstWindow_Click"/>

</Grid>

**

public partial class Window1 : Window

{
private Button btnfirstWindow;

public Window1(Button btnfirstWindow)

{
this.btnfirstWindow = btnfirstWindow;

InitializeComponent();
}

private void Window_Loaded(object sender, RoutedEventArgs e)
{
btnfirstWindow.Click += btnfirstWindow_Click;
}

void btnfirstWindow_Click(object sender, RoutedEventArgs e)
{
lblShowUser.Background = Brushes.Red;
}

}

** Window1 XAML**

Title="Window1" Height="450" Width="800">

<Grid>
<Label Name="lblShowUser" Content="Label" HorizontalAlignment="Left" Height="119" Margin="321,98,0,0" VerticalAlignment="Top" Width="281"/>

</Grid>

 

[Skydiver]

You already have a thread about this exact same topic. Closing this thread.