Added an option to specify classes

src/Avalonia.Controls/Notifications/IManagedNotificationManager.cs

@@ -23,10 +23,12 @@ namespace Avalonia.Controls.Notifications
         /// <param name="expiration">the expiration time of the notification after which it will automatically close. If the value is <see cref="TimeSpan.Zero"/> then the notification will remain open until the user closes it.</param>
         /// <param name="onClick">an Action to be run when the notification is clicked.</param>
         /// <param name="onClose">an Action to be run when the notification is closed.</param>
+        /// <param name="classes">Style-classes to ba added to the notification card</param>
         void Show(object content,
             NotificationType type = NotificationType.Information,
             TimeSpan? expiration = null,
             Action? onClick = null,
-            Action? onClose = null);
+            Action? onClose = null, 
+            string[]? classes = null);
     }
 }

src/Avalonia.Controls/Notifications/WindowNotificationManager.cs

@@ -88,7 +88,8 @@ namespace Avalonia.Controls.Notifications
             NotificationType type = NotificationType.Information, 
             TimeSpan? expiration = null,
             Action? onClick = null, 
-            Action? onClose = null)
+            Action? onClose = null, 
+            string[]? classes = null)
         {
             var notificationControl = new NotificationCard
             {
@@ -96,6 +97,15 @@ namespace Avalonia.Controls.Notifications
                 NotificationType = type
             };
 
+            // Add style classes if any
+            if (classes != null)
+            {
+                foreach (var @class in classes)
+                {
+                    notificationControl.Classes.Add(@class);
+                }
+            }
+            
             notificationControl.NotificationClosed += (sender, args) =>
             {
                 onClose?.Invoke();