fix opacity on scrollviewer

Author: ButchersBoy

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.ScrollViewer.xaml

@@ -23,7 +23,7 @@
                 </DoubleAnimationUsingKeyFrames>
             </Storyboard>
         </ControlTemplate.Resources>
-        <Grid x:Name="Grid" Background="{TemplateBinding Background}" Opacity="0.56">
+        <Grid x:Name="Grid" Background="{TemplateBinding Background}">
             <Grid.ColumnDefinitions>
                 <ColumnDefinition Width="*"/>
                 <ColumnDefinition Width="Auto"/>