Fix the StatusStripSizingGrip.

Author: KlausLoeffelmann

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripRenderer.cs

@@ -1044,4 +1044,26 @@ private static Bitmap CreateDisabledImage(Image normalImage, ImageAttributes? im
 
         return disabledBitmap;
     }
+
+    private protected static int GetCornerOffset(ToolStrip toolStrip)
+    {
+        // If we're on Windows 11, offset slightly to avoid hitting rounded corners,
+        // _if_ we are at all dealing with rounded corners.
+        int cornerOffset = 3;
+
+        if (Environment.OSVersion.Version >= new Version(10, 0, 22000)
+            && toolStrip.FindForm() is Form f)
+        {
+#pragma warning disable WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
+            cornerOffset = f.FormCornerPreference switch
+            {
+                FormCornerPreference.Round => 8,
+                FormCornerPreference.RoundSmall => 5,
+                _ => 3
+            };
+#pragma warning restore WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
+        }
+
+        return cornerOffset;
+    }
 }

src/System.Windows.Forms/System/Windows/Forms/Controls/ToolStrips/ToolStripSystemDarkModeRenderer.cs

@@ -718,13 +718,14 @@ protected override void OnRenderStatusStripSizingGrip(ToolStripRenderEventArgs e
         Rectangle bounds = e.AffectedBounds;
         Graphics g = e.Graphics;
 
-        // Draw a dark mode sizing grip
-        Color darkColor = GetDarkModeColor(SystemColors.ControlDark);
-        Color lightColor = GetDarkModeColor(SystemColors.ControlLight);
+        // Use better contrast for dark mode
+        Color shadowColor = GetDarkModeColor(SystemColors.ButtonShadow);
+        Color highlightColor = GetDarkModeColor(SystemColors.ButtonHighlight);
+
+        int cornerOffset = GetCornerOffset(e.ToolStrip);
 
-        // Start at the bottom-right corner and move up and left
-        int x = bounds.Right - 3;
-        int y = bounds.Bottom - 3;
+        int x = bounds.Right - cornerOffset;
+        int y = bounds.Bottom - cornerOffset;
 
         for (int i = 0; i < 3; i++)
         {
@@ -733,8 +734,8 @@ protected override void OnRenderStatusStripSizingGrip(ToolStripRenderEventArgs e
 
             for (int j = 0; j <= i; j++)
             {
-                g.FillRectangle(new SolidBrush(darkColor), tempX, tempY, 2, 2);
-                g.FillRectangle(new SolidBrush(lightColor), tempX - 1, tempY - 1, 1, 1);
+                g.FillRectangle(new SolidBrush(shadowColor), tempX, tempY, 2, 2);
+                g.FillRectangle(new SolidBrush(highlightColor), tempX - 1, tempY - 1, 1, 1);
 
                 tempX -= 4;
                 tempY += 4;