Merge pull request #1587 from MicrosoftDocs/chigy/style

Update style section to talk about the knob to utilize previous version

Author: Court72

windows-apps-src/design/controls-and-patterns/xaml-styles.md

@@ -19,6 +19,23 @@ ms.localizationpriority: medium
 
 You can customize the appearance of your apps in many ways by using the XAML framework. Styles let you set control properties and reuse those settings for a consistent appearance across multiple controls.
 
+## WinUI and styles
+
+Starting with WinUI 2.2, we have used the [Windows UI Library](/windows/apps/winui/) (WinUI) to deliver new visual style updates across our UI components. If you notice your UI is not updating to the latest styles, be sure to update to the latest WinUI NuGet package.
+
+Starting with WinUI 2.6, we provide new styles for most of the controls, and a new versioning system that let's you revert to the previous control styles if needed. We encourage you to use the new styles, as they better match the design direction of Windows. However, if your scenario cannot support the new styles, the previous versions are still available.
+
+You can change the style version by setting the `ControlsResourcesVersion` property on the `XamlControlsResources` that you include in your `Application.Resources` when you use WinUI version 2. `ControlsResourcesVersion` defaults to the enum value `Version2`.
+
+Setting this value to `Version1` causes `XamlControlsResources` to load the previous style versions instead of the new styles used by the latest WinUI version. Changing this property at runtime is not supported and VisualStudio's hot reload functionality will not work; however, after you rebuild your application you will see the control styles change.
+
+```xaml
+<Application.Resources>
+    <XamlControlsResources xmlns="using:Microsoft.UI.Xaml.Controls" 
+                           ControlsResourcesVersion="Version1"/>
+</Application.Resources>
+```
+
 ## Style basics
 
 Use styles to extract visual property settings into reusable resources. Here's an example that shows 3 buttons with a style that sets the [BorderBrush](/uwp/api/windows.ui.xaml.controls.control.borderbrush), [BorderThickness](/uwp/api/windows.ui.xaml.controls.control.borderthickness) and [Foreground](/uwp/api/windows.ui.xaml.controls.control.foreground) properties. By applying a style, you can make the controls appear the same without having to set these properties on each control separately.
@@ -202,4 +219,4 @@ You should use the styles that come from the Windows Runtime default XAML resour
 
 ## The template property
 
-A style setter can be used for the [Template](/uwp/api/windows.ui.xaml.controls.control.template) property of a [Control](/uwp/api/Windows.UI.Xaml.Controls.Control), and in fact this makes up the majority of a typical XAML style and an app's XAML resources. This is discussed in more detail in the topic [Control templates](control-templates.md).
+A style setter can be used for the [Template](/uwp/api/windows.ui.xaml.controls.control.template) property of a [Control](/uwp/api/Windows.UI.Xaml.Controls.Control), and in fact this makes up the majority of a typical XAML style and an app's XAML resources. This is discussed in more detail in the topic [Control templates](control-templates.md).

windows-apps-src/design/style/index.md

@@ -14,6 +14,8 @@ ms.custom: RS5
 
 Style is what makes your app stand out. The style guidelines in this section help you create a Fluent Design through color, typography, and new features such as acrylic material and reveal highlight.
 
+We use the [Windows UI Library](/windows/apps/winui/) (WinUI) to deliver the latest styles across our UI components. Be sure to use the latest WinUI version to keep your apps up-to-date with the current Windows app Fluent styles. For more info about how to do this, see [XAML styles](../controls-and-patterns/xaml-styles.md).
+
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 ![Image depicting a color gradient.](images/header-color.svg)