Ensure the flyout respects the given RequestedTheme... although it doesn't seem to be picking up the theme changes from Windows user settings just yet...

NotificationFlyout.Sample/NotificationFlyoutPresenter.xaml

@@ -3,34 +3,12 @@
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:controls="using:NotificationFlyout.Uwp.UI.Controls"
-    CornerRadius="8">
+    CornerRadius="4"
+    RequestedTheme="Default">
     <Grid
         Width="330"
         Height="360"
         Margin="23">
-        <Grid.RowDefinitions>
-            <RowDefinition Height="Auto" />
-            <RowDefinition Height="Auto" />
-        </Grid.RowDefinitions>
-        <TextBlock Text="Quick lauch" />
-        <GridView Grid.Row="1" HorizontalAlignment="Center">
-            <GridView.ItemsPanel>
-                <ItemsPanelTemplate>
-                    <ItemsWrapGrid Orientation="Horizontal" />
-                </ItemsPanelTemplate>
-            </GridView.ItemsPanel>
-            <Button
-                Width="94"
-                Margin="6,6,3,6"
-                Content="Test" />
-            <Button
-                Width="94"
-                Margin="3,6,3,6"
-                Content="Test" />
-            <Button
-                Width="94"
-                Margin="3,6,6,6"
-                Content="Test" />
-        </GridView>
+        <ToggleSwitch x:Name="test" Toggled="ToggleSwitch_Toggled" />
     </Grid>
 </controls:NotificationFlyoutPresenter>

NotificationFlyout.Sample/NotificationFlyoutPresenter.xaml.cs

@@ -6,5 +6,18 @@
         {
             InitializeComponent();
         }
+
+        private void ToggleSwitch_Toggled(object sender, Windows.UI.Xaml.RoutedEventArgs e)
+        {
+            if (test.IsOn)
+            {
+                this.RequestedTheme = Windows.UI.Xaml.ElementTheme.Dark;
+            }
+            else
+            {
+                this.RequestedTheme = Windows.UI.Xaml.ElementTheme.Light;
+
+            }
+        }
     }
 }

NotificationFlyout.Tray/SampleNotificationFlyout.xaml

@@ -3,6 +3,7 @@
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:sample="clr-namespace:NotificationFlyout.Sample;assembly=NotificationFlyout.Sample"
-    IconSource="/Assets/Icon.ico">
+    IconSource="/Assets/Icon.ico"
+    LightIconSource="/Assets/Icon.ico">
     <sample:NotificationFlyoutPresenter />
 </NotificationFlyout>

NotificationFlyout.Uwp.UI.Controls/NotificationFlyoutPresenter/NotificationFlyoutPresenter.xaml

@@ -2,8 +2,19 @@
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:controls="using:NotificationFlyout.Uwp.UI.Controls">
+    <ResourceDictionary.ThemeDictionaries>
+        <ResourceDictionary x:Key="Default">
+            <StaticResource x:Key="NotificationFlyoutPresenterBackground" ResourceKey="SystemControlTransientBackgroundBrush" />
+        </ResourceDictionary>
+        <ResourceDictionary x:Key="HighContrast">
+            <StaticResource x:Key="NotificationFlyoutPresenterBackground" ResourceKey="SystemControlPageBackgroundChromeMediumLowBrush" />
+        </ResourceDictionary>
+        <ResourceDictionary x:Key="Light">
+            <StaticResource x:Key="NotificationFlyoutPresenterBackground" ResourceKey="SystemControlTransientBackgroundBrush" />
+        </ResourceDictionary>
+    </ResourceDictionary.ThemeDictionaries>
     <Style TargetType="controls:NotificationFlyoutPresenter">
-        <Setter Property="Background" Value="{StaticResource SystemControlTransientBackgroundBrush}" />
+        <Setter Property="Background" Value="{ThemeResource SystemControlTransientBackgroundBrush}" />
         <Setter Property="Template">
             <Setter.Value>
                 <ControlTemplate TargetType="controls:NotificationFlyoutPresenter">

NotificationFlyout.Wpf.UI.Controls/NotificationFlyout/NotificationFlyout.cs

@@ -81,6 +81,11 @@ namespace NotificationFlyout.Wpf.UI.Controls
         }
 
         private void OnIconPropertyChanged()
+        {
+            SetIcon();
+        }
+
+        private void SetIcon()
         {
             var shellTrayHandle = WindowHelper.GetHandle(ShellTrayHandleName);
             if (shellTrayHandle == null) return;
@@ -88,8 +93,9 @@ namespace NotificationFlyout.Wpf.UI.Controls
             var dpi = WindowHelper.GetDpi(shellTrayHandle);
 
             var iconSource = SystemSettingsHelper.DefaultSystemTheme == SystemTheme.Dark ? IconSource : LightIconSource;
-            using var icon = iconSource.ConvertToIcon(dpi);
+            if (iconSource == null) return;
 
+            using var icon = iconSource.ConvertToIcon(dpi);
             _xamlHost.SetNotificationIcon(icon.Handle);
         }
     }