Get Appplication.Resources from StaticResource.

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/StaticResourceExtension.cs

@@ -4,6 +4,7 @@
 using System;
 using System.ComponentModel;
 using Avalonia.Controls;
+using Avalonia.Styling;
 using Portable.Xaml;
 using Portable.Xaml.ComponentModel;
 using Portable.Xaml.Markup;
@@ -33,7 +34,14 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
             foreach (IResourceProvider resourceProvider in resourceProviders)
             {
-                if (resourceProvider.TryGetResource(ResourceKey, out var value))
+                if (resourceProvider is IControl control && control.StylingParent != null)
+                {
+                    // If we've got to a control that has a StylingParent then it's probably
+                    // a top level control and its StylingParent is pointing to the global
+                    // styles. If this is case just do a FindResource on it.
+                    return control.FindResource(ResourceKey);
+                }
+                else if (resourceProvider.TryGetResource(ResourceKey, out var value))
                 {
                     return value;
                 }

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/StaticResourceTests.cs

@@ -59,6 +59,28 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
             Assert.Equal(0xff506070, brush.Color.ToUint32());
         }
 
+        [Fact]
+        public void StaticResource_From_Application_Can_Be_Assigned_To_Property_In_Window()
+        {
+            using (StyledWindowNoTheme())
+            {
+                Application.Current.Resources.Add("brush", new SolidColorBrush(0xff506070));
+
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+             xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'>
+    <Border Name='border' Background='{StaticResource brush}'/>
+</Window>";
+
+                var loader = new AvaloniaXamlLoader();
+                var window = (Window)loader.Load(xaml);
+                var border = window.FindControl<Border>("border");
+
+                var brush = (SolidColorBrush)border.Background;
+                Assert.Equal(0xff506070, brush.Color.ToUint32());
+            }
+        }
+
         [Fact]
         public void StaticResource_Can_Be_Assigned_To_Setter()
         {