feat: add appear animation.

src/Ursa/Controls/Dialog/OverlayDialogHost.Dialog.cs

@@ -92,7 +92,7 @@ public partial class OverlayDialogHost
         ResetZIndices();
     }
     
-    private void OnDialogControlClosing(object sender, object? e)
+    private async void OnDialogControlClosing(object sender, object? e)
     {
         if (sender is DialogControlBase control)
         {
@@ -109,6 +109,7 @@ public partial class OverlayDialogHost
                 if (_masks.Count > 0)
                 {
                     var last = _masks.Last();
+                    await _maskDisappearAnimation.RunAsync(last);
                     this.Children.Remove(last);
                     _masks.Remove(last);
                     if (_masks.Count > 0)
@@ -116,6 +117,7 @@ public partial class OverlayDialogHost
                         _masks.Last().IsVisible = true;
                     }
                 }
+                
             }
             ResetZIndices();
         }
@@ -143,33 +145,7 @@ public partial class OverlayDialogHost
         SetToPosition(control);
         control.AddHandler(OverlayFeedbackElement.ClosedEvent, OnDialogControlClosing);
         control.AddHandler(DialogControlBase.LayerChangedEvent, OnDialogLayerChanged);
-    }
+        _maskAppearAnimation.RunAsync(mask);
-    
-    
-
-    private void OnDrawerControlClosing(object sender, ResultEventArgs e)
-    {
-        if (sender is DrawerControlBase control)
-        {
-            Children.Remove(control);
-            control.RemoveHandler(CustomDialogControl.ClosedEvent, OnDialogControlClosing);
-            control.RemoveHandler(CustomDialogControl.LayerChangedEvent, OnDialogLayerChanged);
-            if (_modalDialogs.Contains(control))
-            {
-                _modalDialogs.Remove(control);
-                if (_masks.Count > 0)
-                {
-                    var last = _masks.Last();
-                    this.Children.Remove(last);
-                    _masks.Remove(last);
-                    if (_masks.Count > 0)
-                    {
-                        _masks.Last().IsVisible = true;
-                    }
-                }
-            }
-            ResetZIndices();
-        }
     }
 
     // Handle dialog layer change event

src/Ursa/Controls/Dialog/OverlayDialogHost.Drawer.cs

@@ -4,6 +4,7 @@ using Avalonia.Animation.Easings;
 using Avalonia.Controls;
 using Avalonia.Styling;
 using Ursa.Controls.OverlayShared;
+using Ursa.EventArgs;
 
 namespace Ursa.Controls;
 
@@ -61,4 +62,29 @@ public partial class OverlayDialogHost
         animation.Duration = TimeSpan.FromSeconds(0.3);
         return animation;
     }
+    
+    private void OnDrawerControlClosing(object sender, ResultEventArgs e)
+    {
+        if (sender is DrawerControlBase control)
+        {
+            Children.Remove(control);
+            control.RemoveHandler(OverlayFeedbackElement.ClosedEvent, OnDialogControlClosing);
+            control.RemoveHandler(DialogControlBase.LayerChangedEvent, OnDialogLayerChanged);
+            if (_modalDialogs.Contains(control))
+            {
+                _modalDialogs.Remove(control);
+                if (_masks.Count > 0)
+                {
+                    var last = _masks.Last();
+                    this.Children.Remove(last);
+                    _masks.Remove(last);
+                    if (_masks.Count > 0)
+                    {
+                        _masks.Last().IsVisible = true;
+                    }
+                }
+            }
+            ResetZIndices();
+        }
+    }
 }

src/Ursa/Controls/Dialog/OverlayDialogHost.Shared.cs

@@ -1,10 +1,12 @@
 using Avalonia;
+using Avalonia.Animation;
 using Avalonia.Controls;
 using Avalonia.Controls.Templates;
 using Avalonia.Input;
 using Avalonia.Media;
 using Ursa.Controls.OverlayShared;
 using Avalonia.Layout;
+using Avalonia.Styling;
 
 namespace Ursa.Controls;
 
@@ -13,6 +15,28 @@ public partial class OverlayDialogHost: Canvas
     private readonly List<OverlayFeedbackElement> _dialogs = new();
     private readonly List<OverlayFeedbackElement> _modalDialogs = new(); 
     private readonly List<Border> _masks = new();
+    private static readonly Animation _maskAppearAnimation;
+    private static readonly Animation _maskDisappearAnimation;
+    
+    static OverlayDialogHost()
+    {
+        _maskAppearAnimation = CreateOpacityAnimation(true);
+        _maskDisappearAnimation = CreateOpacityAnimation(false);
+    }
+    
+    private static Animation CreateOpacityAnimation(bool appear)
+    {
+        var animation = new Animation();
+        animation.FillMode = FillMode.Forward;
+        var keyFrame1 = new KeyFrame(){ Cue = new Cue(0.0) };
+        keyFrame1.Setters.Add(new Setter() { Property = OpacityProperty, Value = appear ? 0.0 : 1.0 });
+        var keyFrame2 = new KeyFrame() { Cue = new Cue(1.0) };
+        keyFrame2.Setters.Add(new Setter() { Property = OpacityProperty, Value = appear ? 1.0 : 0.0 });
+        animation.Children.Add(keyFrame1);
+        animation.Children.Add(keyFrame2);
+        animation.Duration = TimeSpan.FromSeconds(0.3);
+        return animation;
+    }
     
     public string? HostId { get; set; }
     

src/Ursa/Controls/Drawer/CustomDrawerControl.cs

@@ -4,8 +4,6 @@ namespace Ursa.Controls;
 
 public class CustomDrawerControl: DrawerControlBase
 {
-    internal bool IsCloseButtonVisible { get; set; }
-    
     protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
     {
         base.OnApplyTemplate(e);

src/Ursa/Controls/Drawer/DrawerControlBase.cs

@@ -40,7 +40,7 @@ public const string PART_CloseButton = "PART_CloseButton";
 
     public static readonly StyledProperty<bool> IsCloseButtonVisibleProperty =
         AvaloniaProperty.Register<DrawerControlBase, bool>(
-            nameof(IsCloseButtonVisible));
+            nameof(IsCloseButtonVisible), defaultValue: true);
 
     public bool IsCloseButtonVisible
     {