Get the OpenPaneLength from the resource

src/Calculator/App.xaml

@@ -333,6 +333,7 @@
 
             <FontFamily x:Key="CalculatorFontFamily">ms-appx:///Assets/CalculatorIcons.ttf#Calculator Fluent Icons</FontFamily>
 
+            <x:Double x:Key="SplitViewOpenPaneLength">256</x:Double>
             <Thickness x:Key="PivotPortraitThemePadding">0,1,0,0</Thickness>
             <x:Double x:Key="PivotHeaderItemFontSize">14</x:Double>
             <FontWeight x:Key="PivotHeaderItemThemeFontWeight">Normal</FontWeight>

src/Calculator/Views/MainPage.xaml.cs

@@ -606,7 +606,7 @@ namespace CalculatorApp
 
         private double NavigationViewOpenPaneLength(bool isAlwaysOnTop)
         {
-            return isAlwaysOnTop ? 0 : 256;
+            return isAlwaysOnTop ? 0 : (double)Application.Current.Resources["SplitViewOpenPaneLength"];
         }
 
         private CalculatorApp.Calculator m_calculator;