Add DialogHost properties and fix crash

Author: mysteryx93

src/MvvmDialogs.Avalonia.DialogHost/DialogHostApi.cs

@@ -25,6 +25,9 @@ internal class DialogHostApi : IDialogHostApi
             host.CloseOnClickAway = settings.CloseOnClickAway;
             host.CloseOnClickAwayParameter = settings.CloseOnClickAwayParameter;
             host.PopupPositioner = settings.PopupPositioner;
+            host.OverlayBackground = settings.OverlayBackground ?? host.OverlayBackground;
+            host.DialogMargin = settings.DialogMargin ?? host.DialogMargin;
+            host.DisableOpeningAnimation = settings.DisableOpeningAnimation;
         }
 
         var closingHandler = settings.ClosingHandler ?? ((_, _) => { });

src/MvvmDialogs.Avalonia.DialogHost/DialogHostSettings.cs

@@ -1,4 +1,5 @@
 using System.ComponentModel;
+using Avalonia.Media;
 using DialogHostAvalonia;
 using DialogHostAvalonia.Positioners;
 
@@ -29,4 +30,16 @@ public class DialogHostSettings : DialogSettingsBase
     /// A class allowing to customize the positioning of the dialog.
     /// </summary>
     public IDialogPopupPositioner? PopupPositioner { get; set; }
+    /// <summary>
+    /// The background of the overlay.
+    /// </summary>
+    public IBrush? OverlayBackground { get; set; }
+    /// <summary>
+    /// The margin of the dialog view.
+    /// </summary>
+    public Thickness? DialogMargin { get; set; }
+    /// <summary>
+    /// Whether to disable the popup animation.
+    /// </summary>
+    public bool DisableOpeningAnimation { get; set; } = true;
 }