feat: support top and bottom icon button.

src/Ursa.Themes.Semi/Converters/BooleansToOpacityConverter.cs

@@ -0,0 +1,21 @@
+using System.Globalization;
+using Avalonia.Data.Converters;
+
+namespace Ursa.Themes.Semi.Converters;
+
+public class BooleansToOpacityConverter: IValueConverter
+{
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (value is bool b)
+        {
+            return b? 1.0: 0.0;
+        }
+        return 1;
+    }
+
+    public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        throw new NotImplementedException();
+    }
+}