Fixed divider widget on WinForms

changes/2667.bugfix.rst

@@ -0,0 +1 @@
+On WinForms, the Divider widget now behaves correctly and allows changing its background_color and dimensions.

winforms/src/toga_winforms/widgets/divider.py

@@ -1,17 +1,17 @@
 from decimal import ROUND_UP
 
 import System.Windows.Forms as WinForms
+from System.Drawing import SystemColors
 from travertino.size import at_least
 
 from .base import Widget
 
 
 class Divider(Widget):
     def create(self):
-        self.native = WinForms.Label()
-        self.native.BorderStyle = WinForms.BorderStyle.Fixed3D
+        self.native = WinForms.Panel()
         self.native.AutoSize = False
-
+        self._default_background = SystemColors.ControlDark
         self._direction = self.interface.HORIZONTAL
 
     def get_direction(self):
@@ -20,11 +20,11 @@ def get_direction(self):
     def set_direction(self, value):
         self._direction = value
         if value == self.interface.HORIZONTAL:
-            self.native.Height = 2
+            self.native.Height = 1
             self.native.Width = 0
         else:
             self.native.Height = 0
-            self.native.Width = 2
+            self.native.Width = 1
 
     def rehint(self):
         if self.get_direction() == self.interface.HORIZONTAL:

winforms/tests_backend/widgets/divider.py

@@ -4,4 +4,4 @@
 
 
 class DividerProbe(SimpleProbe):
-    native_class = System.Windows.Forms.Label
+    native_class = System.Windows.Forms.Panel