support for .NET framework 3.5

Still have bugs

Net35/HandyControl_Net35/Tools/StyleSelector/TabItemCapsuleStyleSelector.cs

@@ -0,0 +1,30 @@
+using System.Windows;
+using System.Windows.Controls;
+using HandyControl.Data;
+
+namespace HandyControl.Tools
+{
+    public class TabItemCapsuleStyleSelector : StyleSelector
+    {
+        public override Style SelectStyle(object item, DependencyObject container)
+        {
+            if (item is TabItem tabItem && tabItem.Parent is TabControl tabControl)
+            {
+                var count = tabControl.Items.Count;
+                if (count == 1)
+                {
+                    return ResourceHelper.GetResource<Style>(ResourceToken.TabItemCapsuleSingle);
+                }
+
+                var index = tabControl.Items.IndexOf(tabItem);
+                return index == 0
+                    ? ResourceHelper.GetResource<Style>(ResourceToken.TabItemCapsuleHorizontalFirst)
+                    : ResourceHelper.GetResource<Style>(index == count - 1
+                        ? ResourceToken.TabItemCapsuleHorizontalLast
+                        : ResourceToken.TabItemCapsuleDefault);
+            }
+
+            return null;
+        }
+    }
+}