Fix CheckBox/RadioButton Appearance.Button + FlatStyle.Standard invisible in dark mode

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonInternal/CheckBoxStandardAdapter.cs

@@ -89,7 +89,7 @@ internal override Size GetPreferredSizeCore(Size proposedSize)
     {
         if (Control.Appearance == Appearance.Button)
         {
-            ButtonStandardAdapter adapter = new(Control);
+            ButtonBaseAdapter adapter = DarkModeAdapterFactory.CreateStandardAdapter(Control);
             return adapter.GetPreferredSizeCore(proposedSize);
         }
         else
@@ -105,9 +105,9 @@ internal override Size GetPreferredSizeCore(Size proposedSize)
         }
     }
 
-    private new ButtonStandardAdapter ButtonAdapter => (ButtonStandardAdapter)base.ButtonAdapter;
+    private new ButtonBaseAdapter ButtonAdapter => base.ButtonAdapter;
 
-    protected override ButtonBaseAdapter CreateButtonAdapter() => new ButtonStandardAdapter(Control);
+    protected override ButtonBaseAdapter CreateButtonAdapter() => DarkModeAdapterFactory.CreateStandardAdapter(Control);
 
     protected override LayoutOptions Layout(PaintEventArgs e)
     {

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonInternal/DarkMode/ButtonDarkModeAdapter.cs

@@ -158,22 +158,28 @@ internal override void PaintOver(PaintEventArgs e, CheckState state)
             g.SmoothingMode = Drawing.Drawing2D.SmoothingMode.AntiAlias;
 
             LayoutData layout = CommonLayout().Layout();
+
+            // A checked toggle-button must remain visually pressed even on hover.
+            PushButtonState pushButtonState = state == CheckState.Checked
+                ? PushButtonState.Pressed
+                : PushButtonState.Hot;
+
             ButtonDarkModeRenderer.RenderButton(
                 g,
                 Control.ClientRectangle,
                 Control.FlatStyle,
-                PushButtonState.Hot,
+                pushButtonState,
                 Control.IsDefault,
                 Control.Focused,
                 Control.ShowFocusCues,
                 Control.Parent?.BackColor ?? Control.BackColor,
-                GetButtonBackColor(PushButtonState.Hot),
+                GetButtonBackColor(pushButtonState),
                 _ => PaintImage(e, layout),
                 () => PaintField(
                     e,
                     layout,
                     PaintDarkModeRender(e).Calculate(),
-                    GetButtonTextColor(e, PushButtonState.Hot),
+                    GetButtonTextColor(e, pushButtonState),
                     drawFocus: false)
             );
 

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/ButtonInternal/RadioButtonStandardAdapter.cs

@@ -50,9 +50,9 @@ internal override void PaintOver(PaintEventArgs e, CheckState state)
         }
     }
 
-    private new ButtonStandardAdapter ButtonAdapter => (ButtonStandardAdapter)base.ButtonAdapter;
+    private new ButtonBaseAdapter ButtonAdapter => base.ButtonAdapter;
 
-    protected override ButtonBaseAdapter CreateButtonAdapter() => new ButtonStandardAdapter(Control);
+    protected override ButtonBaseAdapter CreateButtonAdapter() => DarkModeAdapterFactory.CreateStandardAdapter(Control);
 
     protected override LayoutOptions Layout(PaintEventArgs e)
     {

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/CheckBox.cs

@@ -96,17 +96,7 @@ public Appearance Appearance
         }
     }
 
-    private protected override bool OwnerDraw =>
-            // We want NO owner draw ONLY when we're
-            // * In Dark Mode
-            // * When _then_ the Appearance is Button
-            // * But then ONLY when we're rendering with FlatStyle.Standard
-            //   (because that would let us usually let us draw with the VisualStyleRenderers,
-            //   which cause HighDPI issues in Dark Mode).
-            (!Application.IsDarkModeEnabled
-                || Appearance != Appearance.Button
-                || FlatStyle != FlatStyle.Standard)
-                && base.OwnerDraw;
+    private protected override bool OwnerDraw => base.OwnerDraw;
 
     [SRCategory(nameof(SR.CatPropertyChanged))]
     [SRDescription(nameof(SR.CheckBoxOnAppearanceChangedDescr))]

src/System.Windows.Forms/System/Windows/Forms/Controls/Buttons/RadioButton.cs

@@ -173,18 +173,7 @@ public bool Checked
         }
     }
 
-    private protected override bool OwnerDraw =>
-        // Order is key here - do NOT change!
-        // We want NO owner draw ONLY when we're
-        // * in Dark Mode
-        // * when _then_ the Appearance is Button
-        // * but then ONLY when we're rendering with FlatStyle.Standard
-        //   (because that would let us usually let us draw with the VisualStyleRenderers,
-        //   which cause HighDPI issues in Dark Mode).
-        (!Application.IsDarkModeEnabled
-            || Appearance != Appearance.Button
-            || FlatStyle != FlatStyle.Standard)
-            && base.OwnerDraw;
+    private protected override bool OwnerDraw => base.OwnerDraw;
 
     /// <hideinheritance/>
     [Browsable(false)]

src/test/unit/System.Windows.Forms/System/Windows/Forms/CheckBoxTests.cs

@@ -631,6 +631,31 @@ public void CheckBox_ToStringTest()
         Assert.Equal(expected, actual);
     }
 
+#pragma warning disable SYSLIB5002 // Type is for evaluation purposes only and is subject to change or removal in future updates.
+    [WinFormsFact]
+    public void CheckBox_OwnerDraw_AppearanceButton_FlatStyleStandard_InDarkMode_IsTrue()
+    {
+        // Regression test for https://github.com/dotnet/winforms/issues/14347:
+        // CheckBox with Appearance.Button + FlatStyle.Standard must always use owner-draw,
+        // including in dark mode. If OwnerDraw returns false the control falls back to
+        // native ComCtl32 painting which renders an invisible button on dark backgrounds.
+        Application.SetColorMode(SystemColorMode.Dark);
+        try
+        {
+            using SubCheckBox control = new()
+            {
+                Appearance = Appearance.Button,
+                FlatStyle = FlatStyle.Standard
+            };
+            Assert.True(control.GetStyle(ControlStyles.UserPaint));
+        }
+        finally
+        {
+            Application.SetColorMode(SystemColorMode.Classic);
+        }
+    }
+#pragma warning restore SYSLIB5002
+
     public class SubCheckBox : CheckBox
     {
         public new bool CanEnableIme => base.CanEnableIme;

src/test/unit/System.Windows.Forms/System/Windows/Forms/RadioButtonTests.cs

@@ -1665,5 +1665,30 @@ internal override bool RaiseAutomationPropertyChangedEvent(UIA_PROPERTY_ID prope
     [InlineData(Appearance.Normal, FlatStyle.System)]
     public void RadioButton_OverChangeRectangle_Get(Appearance appearance, FlatStyle flatStyle) => base.ButtonBase_OverChangeRectangle_Get(appearance, flatStyle);
 
+#pragma warning disable SYSLIB5002 // Type is for evaluation purposes only and is subject to change or removal in future updates.
+    [WinFormsFact]
+    public void RadioButton_OwnerDraw_AppearanceButton_FlatStyleStandard_InDarkMode_IsTrue()
+    {
+        // Regression test for https://github.com/dotnet/winforms/issues/14347:
+        // RadioButton with Appearance.Button + FlatStyle.Standard must always use owner-draw,
+        // including in dark mode. If OwnerDraw returns false the control falls back to
+        // native ComCtl32 painting which renders an invisible button on dark backgrounds.
+        Application.SetColorMode(SystemColorMode.Dark);
+        try
+        {
+            using SubRadioButton control = new()
+            {
+                Appearance = Appearance.Button,
+                FlatStyle = FlatStyle.Standard
+            };
+            Assert.True(control.GetStyle(ControlStyles.UserPaint));
+        }
+        finally
+        {
+            Application.SetColorMode(SystemColorMode.Classic);
+        }
+    }
+#pragma warning restore SYSLIB5002
+
     protected override ButtonBase CreateButton() => new SubRadioButton();
 }