Update Slider.xaml

src/Avalonia.Themes.Default/Slider.xaml

@@ -4,7 +4,7 @@
     <Setter Property="MinHeight" Value="20"/>
     <Setter Property="Template">
       <ControlTemplate>
-        <Grid>
+        <Grid Name="grid">
           <Grid.RowDefinitions>
             <RowDefinition Height="Auto"/>
             <RowDefinition Height="Auto" MinHeight="20"/>
@@ -20,7 +20,7 @@
                <RepeatButton Name="PART_IncreaseButton"
                              Classes="repeattrack" />
             </Track.IncreaseButton>
-            <Thumb MinWidth="20" MinHeight="20">
+            <Thumb Name="thumb" MinWidth="20" MinHeight="20">
               <Thumb.Template>
                 <ControlTemplate>
                   <Grid>
@@ -55,7 +55,7 @@
                <RepeatButton Name="PART_IncreaseButton"
                              Classes="repeattrack" />
             </Track.IncreaseButton>
-            <Thumb MinWidth="20" MinHeight="20">
+            <Thumb Name="thumb" MinWidth="20" MinHeight="20">
               <Thumb.Template>
                 <ControlTemplate>
                   <Grid>
@@ -87,4 +87,7 @@
         </ControlTemplate>
     </Setter>
   </Style>
+    <Style Selector="Slider:disabled /template/ Grid#grid">
+        <Setter Property="Opacity" Value="{DynamicResource ThemeDisabledOpacity}" />
+    </Style>
 </Styles>