Initial WinUI switch.

Wino.Mail.WinUI/Selectors/MailItemContainerStyleSelector.cs

@@ -0,0 +1,18 @@
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+using Wino.Mail.ViewModels.Data;
+
+namespace Wino.Selectors;
+
+public partial class MailItemContainerStyleSelector : StyleSelector
+{
+    public Style Thread { get; set; }
+
+    protected override Style SelectStyleCore(object item, DependencyObject container)
+    {
+        if (item is ThreadMailItemViewModel)
+            return Thread;
+        else
+            return base.SelectStyleCore(item, container);
+    }
+}