Fix BusyDecorator foreground color in dark mode

QuickLook/Controls/BusyDecorator/BusyDecorator.xaml

@@ -11,9 +11,10 @@
                             <ControlTemplate TargetType="{x:Type Control}">
                                 <busyDecorator:SpinIcon FontFamily="{StaticResource SegoeFluent}"
                                                         FontSize="40"
-                                                        Spin="True">
-                                    &#xE72C;
-                                </busyDecorator:SpinIcon>
+                                                        Foreground="{DynamicResource TextFillColorPrimaryBrush}"
+                                                        Opacity="0.9"
+                                                        Spin="True"
+                                                        Text="&#xE72C;" />
                             </ControlTemplate>
                         </Setter.Value>
                     </Setter>

QuickLook/Controls/BusyDecorator/SpinIcon.cs

@@ -47,7 +47,6 @@ internal class SpinIcon : TextBlock, ISpinable
     public bool Spin
     {
         get => (bool)GetValue(SpinProperty);
-
         set => SetValue(SpinProperty, value);
     }
 
@@ -64,9 +63,7 @@ internal class SpinIcon : TextBlock, ISpinable
 
     private static void SpinDurationChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
     {
-        var b = d as SpinIcon;
-
-        if (null == b || !b.Spin || !(e.NewValue is double) ||
+        if (d is not SpinIcon b || !b.Spin || e.NewValue is not double ||
             e.NewValue.Equals(e.OldValue)) return;
 
         b.StopSpin();
@@ -79,7 +76,6 @@ internal class SpinIcon : TextBlock, ISpinable
     public double SpinDuration
     {
         get => (double)GetValue(SpinDurationProperty);
-
         set => SetValue(SpinDurationProperty, value);
     }