I would like to use C#, with no XAML, to have my Avalonia Button display a different background color while it is pressed. Creating Styles for :pointerover and :pressed work for changing the foreground color. But I can’t make it work for the background color for the :pressed pseudoclass. The foreground changes as I’ve specified, but the background turns to the same dark gray one sees when not using any style settings.

Here’s my code:

using Avalonia;
using Avalonia.Controls;
using Avalonia.Controls.Metadata;
using Avalonia.Media;
using Avalonia.Styling;

class MainClass
{
    public static void Main(string[] args) {
        AppBuilder
            .Configure<Application>()
            .UsePlatformDetect()
            .Start(AppMain, args);
    }

    public static void AppMain(Application app, string[] args)
    {
        app.Styles.Add(new Avalonia.Themes.Simple.SimpleTheme());
        app.RequestedThemeVariant = Avalonia.Styling.ThemeVariant.Default;

        var win = new Window
        {
            Width = 128,
            Height = 72,
        };

        Button button = new Button
        {
            Content = "Press",
            FontSize = 24,
        };

        button.Styles.Add(
            new Style(x => x.OfType<Button>().Class(":pointerover")) 
            {
                Setters = 
                {
                    new Setter(Button.BackgroundProperty, Brushes.Green), // This works.
                    new Setter(Button.ForegroundProperty, Brushes.Yellow),
                }
            });

        button.Styles.Add(
            new Style(x => x.OfType<Button>().Class(":pressed")) 
            {
                Setters = 
                {
                    new Setter(Button.BackgroundProperty, Brushes.Blue), // This has no effect.
                    new Setter(Button.ForegroundProperty, Brushes.Red),
                }
            });

        win.Content = button;
        win.Show();
        app.Run(win);
    }
}

And here’s the button in a small window, first with the pointer outside the window, then inside, then inside and pressed:

Any idea how I can get the background to change when pressed?