Make failing test pass.

src/Perspex.Themes.Default/Accents/BaseLight.paml

@@ -27,8 +27,10 @@
     <Color x:Key="SystemListLowColor">#19FFFFFF</Color>
     <Color x:Key="SystemListMediumColor">#33FFFFFF</Color>
 
-    <!-- Assigning StyleResource to non-controls currently fails -->
+    <Color x:Key="FooColor">Red</Color>
+
     <!--<mut:SolidColorBrush x:Key="SystemControlBackgroundBaseHighBrush" Color="{StyleResource SystemBaseHighColor}"/>
-    <mut:SolidColorBrush x:Key="SystemControlBackgroundBaseLowBrush" Color="{StyleResource SystemBaseLowColor}"/>-->
+    <mut:SolidColorBrush x:Key="SystemControlBackgroundBaseLowBrush" Color="{StyleResource SystemBaseLowColor}"/>
+    <mut:SolidColorBrush x:Key="FooBrush" Color="{StyleResource FooColor}"/>-->
   </Style.Resources>
 </Style>

tests/Perspex.Markup.Xaml.UnitTests/Xaml/StyleTests.cs

@@ -134,13 +134,20 @@ namespace Perspex.Markup.Xaml.UnitTests.Xaml
             </Style.Resources>
         </Style>
     </Window.Styles>
+    <Button Name='button' Background='{StyleResource brush}'/>
 </Window>";
 
                 var loader = new PerspexXamlLoader();
                 var window = (Window)loader.Load(xaml);
                 var brush = (Perspex.Media.Mutable.SolidColorBrush)window.FindStyleResource("brush");
+                var button = window.FindControl<Button>("button");
+
+                DelayedBinding.ApplyBindings(button);
+
+                var buttonBrush = (Perspex.Media.Mutable.SolidColorBrush)button.Background;
 
                 Assert.Equal(0xff506070, brush.Color.ToUint32());
+                Assert.Equal(0xff506070, buttonBrush.Color.ToUint32());
             }
         }
     }