Added a theme listener, separate light/dark theme error styles, and property that returns the respective theme.

resolves #3545

Author: winston-de

Microsoft.Toolkit.Uwp.SampleApp/Controls/XamlCodeEditor.xaml.cs

@@ -21,6 +21,8 @@ public sealed partial class XamlCodeEditor : UserControl
         public static readonly DependencyProperty TextProperty =
             DependencyProperty.Register(nameof(Text), typeof(string), typeof(XamlCodeEditor), new PropertyMetadata(string.Empty));
 
+        private ThemeListener _themeListener = new ThemeListener();
+
         public XamlCodeEditor()
         {
             this.InitializeComponent();
@@ -40,7 +42,7 @@ public async void ReportError(XamlExceptionRange error)
             // Highlight Error Line
             XamlCodeRenderer.Decorations.Add(new IModelDeltaDecoration(
                 range,
-                new IModelDecorationOptions() { IsWholeLine = true, ClassName = _errorStyle, HoverMessage = new string[] { error.Message }.ToMarkdownString() }));
+                new IModelDecorationOptions() { IsWholeLine = true, ClassName = ErrorStyle, HoverMessage = new string[] { error.Message }.ToMarkdownString() }));
 
             // Show Glyph Icon
             XamlCodeRenderer.Decorations.Add(new IModelDeltaDecoration(
@@ -121,10 +123,13 @@ public string Text
 
         public DateTime TimeSampleEditedLast { get; private set; } = DateTime.MinValue;
 
-        private CssLineStyle _errorStyle = new CssLineStyle()
+        private CssLineStyle _errorStyle_Light = new CssLineStyle() { BackgroundColor = new SolidColorBrush(Color.FromArgb(0x00, 0xFF, 0xD6, 0xD6)) };
+        private CssLineStyle _errorStyle_Dark = new CssLineStyle() { BackgroundColor = new SolidColorBrush(Color.FromArgb(0x00, 0x6E, 0x00, 0x00)) };
+
+        private CssLineStyle ErrorStyle
         {
-            BackgroundColor = new SolidColorBrush(Color.FromArgb(0x00, 0xFF, 0xD6, 0xD6))
-        };
+            get => _themeListener.CurrentTheme.Equals(ApplicationTheme.Light) ? _errorStyle_Light : _errorStyle_Dark;
+        }
 
         private CssGlyphStyle _errorIconStyle = new CssGlyphStyle()
         {