Updated NumericUpDown style

src/Avalonia.Themes.Default/NumericUpDown.xaml

@@ -1,8 +1,9 @@
 <Styles xmlns="https://github.com/avaloniaui">
   <Style Selector="NumericUpDown">
+    <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}" />
     <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderMidBrush}"/>
     <Setter Property="BorderThickness" Value="{DynamicResource ThemeBorderThickness}"/>
-    <Setter Property="Background" Value="{DynamicResource ThemeBackgroundBrush}" />
+    <Setter Property="Padding" Value="4"/>
     <Setter Property="Template">
       <ControlTemplate>
         <ButtonSpinner Name="PART_Spinner"
@@ -16,7 +17,7 @@
                        ButtonSpinnerLocation="{TemplateBinding ButtonSpinnerLocation}">
           <TextBox Name="PART_TextBox"
                    BorderThickness="0"
-                   Background="Transparent"
+                   Background="{TemplateBinding Background}" 
                    BorderBrush="{TemplateBinding BorderBrush}"
                    Padding="{TemplateBinding Padding}"
                    Watermark="{TemplateBinding Watermark}"
@@ -31,7 +32,6 @@
     </Setter>
   </Style>
   <Style Selector="NumericUpDown /template/ TextBox#PART_TextBox">
-    <Setter Property="Padding" Value="4"/>
     <Setter Property="Margin" Value="4"/>
     <Setter Property="MinWidth" Value="20"/>
   </Style>