How to create a Rhino Panel with Predefine Size

I am working on creating a Rhino Plug-Inn. And my plugin needs to have a panel that’s open by a command and have a default size.

using Eto.Forms;
using Eto.Drawing;
using Rhino.UI;
using System;

public class CustomPanel : Panel
{
    public CustomPanel()
    {
        // Set size for the panel
        this.Size = new Size(400, 300); // width: 400, height: 300

        // Layout setup
        var layout = new DynamicLayout();
        layout.Spacing = new Size(5, 5);
        
        // Adding a button as an example
        var button = new Button { Text = "Click me" };
        layout.AddRow(button);
        
        // Set layout to the panel
        this.Content = layout;
    }
}

public class MyPlugin : Rhino.PlugIns.PlugIn
{
    public MyPlugin()
    {
        Instance = this;
    }

    public static MyPlugin Instance { get; private set; }

    protected override LoadReturnCode OnLoad(ref string errorMessage)
    {
        Panels.RegisterPanel(this, typeof(CustomPanel), "My Custom Panel", null);
        return LoadReturnCode.Success;
    }

    public static Guid PanelId
    {
        get { return typeof(CustomPanel).GUID; }
    }
}

But, it seems like, it Its opening with a default size of maybe 50*50. I also tried with the MinimumSize property, but no luck.

Does anyone know how to fix this?