feat: several fixes.

src/Ursa.Themes.Semi/Controls/NumberDisplayer.axaml

@@ -14,7 +14,7 @@
                     FontFamily="{TemplateBinding FontFamily}"
                     Background="{TemplateBinding Background}"
                     FontWeight="{TemplateBinding FontWeight}"
-                    FontStyle="{TemplateBinding FontSize}"
+                    FontStyle="{TemplateBinding FontStyle}"
                     FontStretch="{TemplateBinding FontStretch}"
                     Text="{TemplateBinding InternalText, Mode=OneWay}" />
             </ControlTemplate>
@@ -28,7 +28,7 @@
                         FontFamily="{TemplateBinding FontFamily}"
                         Background="{TemplateBinding Background}"
                         FontWeight="{TemplateBinding FontWeight}"
-                        FontStyle="{TemplateBinding FontSize}"
+                        FontStyle="{TemplateBinding FontStyle}"
                         FontStretch="{TemplateBinding FontStretch}"
                         Text="{TemplateBinding InternalText, Mode=OneWay}" />
                 </ControlTemplate>

src/Ursa/AssemblyInfo.cs

@@ -3,3 +3,4 @@ using Avalonia.Metadata;
 [assembly:XmlnsPrefix("https://irihi.tech/ursa", "u")]
 [assembly:XmlnsDefinition("https://irihi.tech/ursa", "Ursa")]
 [assembly:XmlnsDefinition("https://irihi.tech/ursa", "Ursa.Controls")]
+[assembly:XmlnsDefinition("https://irihi.tech/ursa", "Ursa.Controls.Shapes")]

src/Ursa/Controls/NumberDisplayer/Implementations.cs

@@ -62,8 +62,16 @@ public class DateDisplay : NumberDisplayer<DateTime>
         public override DateTime Interpolate(double progress, DateTime oldValue, DateTime newValue)
         {
             var diff = (newValue - oldValue).TotalSeconds;
+            try
+            {
                 return oldValue + TimeSpan.FromSeconds(diff * progress);
             }
+            catch
+            {
+                return oldValue;
+            }
+            
+        }
     }
 
     protected override string GetString(DateTime value)

src/Ursa/Controls/Shapes/PureCircle.cs

@@ -0,0 +1,45 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using Avalonia.Media;
+
+namespace Ursa.Controls.Shapes;
+
+public class PureCircle: Control
+{
+    public static readonly StyledProperty<IBrush?> BackgroundProperty =
+        TemplatedControl.BackgroundProperty.AddOwner<PureCircle>();
+
+    public IBrush? Background
+    {
+        get => GetValue(BackgroundProperty);
+        set => SetValue(BackgroundProperty, value);
+    }
+
+    public static readonly StyledProperty<double> DiameterProperty = AvaloniaProperty.Register<PureCircle, double>(
+        nameof(Diameter));
+
+    public double Diameter
+    {
+        get => GetValue(DiameterProperty);
+        set => SetValue(DiameterProperty, value);
+    }
+
+    static PureCircle()
+    {
+        FocusableProperty.OverrideDefaultValue<PureCircle>(false);
+        AffectsMeasure<PureCircle>(DiameterProperty);
+        AffectsRender<PureCircle>(DiameterProperty, BackgroundProperty);
+    }
+
+    protected override Size MeasureOverride(Size availableSize)
+    {
+        return new Size(Diameter, Diameter);
+    }
+
+    public override void Render(DrawingContext context)
+    {
+        double value = Diameter / 2;
+        context.DrawEllipse(Background, null, new(value, value), value, value);
+    }
+}

src/Ursa/Controls/Shapes/PureRectangle.cs

@@ -1,6 +1,8 @@
 using Avalonia;
 using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
 using Avalonia.Controls.Shapes;
+using Avalonia.Markup.Xaml.Templates;
 using Avalonia.Media;
 
 namespace Ursa.Controls.Shapes;
@@ -10,8 +12,8 @@ namespace Ursa.Controls.Shapes;
 /// </summary>
 public class PureRectangle: Control
 {
-    public static readonly StyledProperty<IBrush?> BackgroundProperty = AvaloniaProperty.Register<PureRectangle, IBrush?>(
+    public static readonly StyledProperty<IBrush?> BackgroundProperty =
-        nameof(Background));
+        TemplatedControl.BackgroundProperty.AddOwner<PureRectangle>();
 
     public IBrush? Background
     {
@@ -21,6 +23,7 @@ public class PureRectangle: Control
     static PureRectangle()
     {
         FocusableProperty.OverrideDefaultValue<PureRectangle>(false);
+        AffectsRender<PureRectangle>(BackgroundProperty);
     }
 
     public override void Render(DrawingContext context)