style<PopupPanel>: add DropShadowEffect

src/Views/About.xaml

@@ -64,6 +64,7 @@
                 Margin="0,24,0,8"
                 Text="{StaticResource Text.About.Title}"
                 HorizontalAlignment="Center"
+                TextOptions.TextFormattingMode="Ideal"
                 FontSize="18" FontWeight="Bold"/>
 
             <!-- Version -->

src/Views/Widgets/PopupPanel.xaml

@@ -18,6 +18,10 @@
             VerticalAlignment="Top"
             Width="500"
             Height="Auto">
+            <Border.Effect>
+                <DropShadowEffect BlurRadius="8" ShadowDepth="0" Opacity=".2" Color="Black"/>
+            </Border.Effect>
+            
             <Grid>                
                 <!-- Custom panel -->
                 <Border x:Name="body">