I would like to change the style of my Avalonia Simple theme slider thumb. If I use the Fluent theme, and add
a Style, I can make it wider. Here’s how it looks in Fluent theme before adding the style:

Here’s how it looks in Fluent theme after adding the style:

Here’s the C# code to make it look like the second picture above:

using Avalonia;
using Avalonia.Controls;
using Avalonia.Styling;
using Avalonia.Controls.Primitives;

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.Fluent.FluentTheme());
        
        var win = new Window { Width = 500, Height = 50, };
        var slider = new Slider { Width = 480, };
        
        slider.Styles.Add(
            new Style(x => x.OfType<Slider>().Descendant().OfType<Thumb>())
            {
                Setters = { new Setter(Thumb.MinWidthProperty, 50.0), }
            });

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

But, if I change this line:

app.Styles.Add(new Avalonia.Themes.Fluent.FluentTheme());

to this line:

app.Styles.Add(new Avalonia.Themes.Simple.SimpleTheme());

which switches from Fluent theme to Simple theme, the slider looks like this:

The style that makes the thumb wider in Fluent theme has no effect on the thumb in Simple theme.

How can I make the thumb wider from C# when I am using Simple theme?