notificationcard default colours are defined as resources

src/Avalonia.Themes.Default/Accents/BaseDark.xaml

@@ -46,6 +46,14 @@
         <SolidColorBrush x:Key="ErrorBrush" Color="{DynamicResource ErrorColor}"></SolidColorBrush>
         <SolidColorBrush x:Key="ErrorLowBrush" Color="{DynamicResource ErrorLowColor}"></SolidColorBrush>
 
+        <SolidColorBrush x:Key="NotificationCardBackgroundBrush" Color="#444444"/>
+        <SolidColorBrush x:Key="NotificationCardInformationBackgroundBrush" Color="Teal"/>
+        <SolidColorBrush x:Key="NotificationCardSuccessBackgroundBrush" Color="LimeGreen"/>
+        <SolidColorBrush x:Key="NotificationCardWarningBackgroundBrush" Color="Orange"/>
+        <SolidColorBrush x:Key="NotificationCardErrorBackgroundBrush" Color="OrangeRed"/>
+
+
+
         <Thickness x:Key="ThemeBorderThickness">1,1,1,1</Thickness>
         <sys:Double x:Key="ThemeDisabledOpacity">0.5</sys:Double>
 

src/Avalonia.Themes.Default/NotificationCard.xaml

@@ -71,18 +71,18 @@
     </Style>
 
     <Style Selector="NotificationCard">
-        <Setter Property="Background" Value="#444444"/>
+        <Setter Property="Background" Value="{DynamicResource NotificationCardBackgroundBrush}"/>
     </Style>
     <Style Selector="NotificationCard:information">
-        <Setter Property="Background" Value="Teal"/>
+        <Setter Property="Background" Value="{DynamicResource NotificationCardInformationBackgroundBrush}"/>
     </Style>
     <Style Selector="NotificationCard:success">
-        <Setter Property="Background" Value="LimeGreen"/>
+        <Setter Property="Background" Value="{DynamicResource NotificationCardSuccessBackgroundBrush}"/>
     </Style>
     <Style Selector="NotificationCard:warning">
-        <Setter Property="Background" Value="Orange"/>
+        <Setter Property="Background" Value="{DynamicResource NotificationCardWarningBackgroundBrush}"/>
     </Style>
     <Style Selector="NotificationCard:error">
-        <Setter Property="Background" Value="OrangeRed"/>
+        <Setter Property="Background" Value="{DynamicResource NotificationCardErrorBackgroundBrush}"/>
     </Style>
 </Styles>