feat: add Content Attribute.

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

@@ -16,7 +16,9 @@
                     <u:Notification Content="Hello, Ursa!" />
                 </u:NotificationCard>
                 <u:NotificationCard NotificationType="Error" Classes="Light">
-                    <u:Notification Title="Welcome" Content="Hello, Ursa!" />
+                    <u:Notification Title="Welcome">
+                        Hello, Ursa!
+                    </u:Notification>
                 </u:NotificationCard>
             </ReversibleStackPanel>
         </ThemeVariantScope>

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

@@ -10,7 +10,9 @@
                     Hello, Ursa!
                 </u:ToastCard>
                 <u:ToastCard NotificationType="Success" Classes="Light">
-                    <u:Toast Content="Hello, Ursa!" />
+                    <u:Toast>
+                        Hello, Ursa!
+                    </u:Toast>
                 </u:ToastCard>
             </ReversibleStackPanel>
         </ThemeVariantScope>

src/Ursa/Controls/Notification/Notification.cs

@@ -1,6 +1,7 @@
 using System.ComponentModel;
 using System.Runtime.CompilerServices;
 using Avalonia.Controls.Notifications;
+using Avalonia.Metadata;
 
 namespace Ursa.Controls;
 
@@ -66,6 +67,7 @@ public class Notification : INotification, INotifyPropertyChanged
     }
 
     /// <inheritdoc/>
+    [Content]
     public string? Content
     {
         get => _content;

src/Ursa/Controls/Toast/Toast.cs

@@ -1,6 +1,7 @@
 using System.ComponentModel;
 using System.Runtime.CompilerServices;
 using Avalonia.Controls.Notifications;
+using Avalonia.Metadata;
 
 namespace Ursa.Controls;
 
@@ -49,6 +50,7 @@ public class Toast : IToast, INotifyPropertyChanged
     }
 
     /// <inheritdoc/>
+    [Content]
     public string? Content
     {
         get => _content;