Since 10.4 VCL styles can be turned on/off per control, see https://blog.marcocantu.com/blog/2020-may-per-control-styling.html.

This makes them suitable for us to get dark mode support for the remaining stuff: our dialogs, other dialogs like message boxes, and tooltips.

Not that in non-dark mode everything is still fully native and unstyled. And in dark mode the main form looks 100% the same as before.

The dark mode style used is 'Window11 Dark 1.0' by Embacadero from GetIt.

Todo:
-Call InitFormTheme in all forms.
-Make TNew* controls aware of VCL styles, or do something else for them.
-Common dialogs look bad in dark mode, at last open file, save file, and open folder.
-Propbaly can revert dark statusbar subclass now.
-Update whatsnew.

Projects/Compil32.dpr

@@ -72,7 +72,9 @@ uses
   IDE.ImagesModule in 'Src\IDE.ImagesModule.pas' {ImagesModule: TDataModule},
   ECDSA in '..\Components\ECDSA.pas',
   ISSigFunc in '..\Components\ISSigFunc.pas',
-  StringScanner in '..\Components\StringScanner.pas';
+  StringScanner in '..\Components\StringScanner.pas',
+  VCL.Styles,
+  VCL.Themes;
 
 {$SETPEOSVERSION 6.1}
 {$SETPESUBSYSVERSION 6.1}
@@ -81,6 +83,7 @@ uses
 {$R Res\Compil32.docicon.res}
 {$R Res\Compil32.manifest.res}
 {$R Res\Compil32.versionandicon.res}
+{$R Res\Compil32.darkstyle.res}
 
 procedure SetAppUserModelID;
 var
@@ -252,6 +255,9 @@ begin
       Title := SCompilerFormCaption;
   end;
 
+  { We don't need VCL Styles for dark menus. This keeps shDialogs and shTooltips. }
+  TStyleManager.SystemHooks := TStyleManager.SystemHooks - [shMenus];
+
   Application.CreateForm(TImagesModule, ImagesModule);
   Application.CreateForm(TMainForm, MainForm);
   Application.Run;

Projects/Src/IDE.HelperFunc.pas

@@ -108,8 +108,11 @@ begin
 end;
 
 procedure SetControlWindowTheme(const WinControl: TWinControl; const Dark: Boolean);
+{ Can be used for buttons to give them the native dark look and for memos and listboxes to give
+  them a native dark scrollbar }
 begin
   if UseThemes then begin
+    WinControl.StyleName := 'Windows';
     if Dark then
       SetWindowTheme(WinControl.Handle, 'DarkMode_Explorer', nil)
     else
@@ -127,29 +130,12 @@ end;
 
 procedure InitFormTheme(Form: TForm);
 
-  procedure InitListBoxDarkTheme(const ListBox: TListBox);
-  begin
-    ListBox.Font.Color := FormTheme.Colors[tcFore];
-    ListBox.Color := FormTheme.Colors[tcBack];
-    ListBox.Invalidate;
-    SetControlWindowTheme(ListBox, FormTheme.Dark);
-  end;
-
   procedure InitWinControlTheme(const ParentControl: TWinControl);
   begin
     for var I := 0 to ParentControl.ControlCount-1 do begin
-      var Control := ParentControl.Controls[I];
-      if Control is TPanel then
-        (Control as TPanel).Color := FormTheme.Colors[tcBack]
-      else if Control is TListBox then
-        InitListBoxDarkTheme(Control as TListBox)
-      else if (Control is TButton) or (Control is TRadioButton) or (Control is TCheckBox) then begin
-        { Not actually used at the moment since only TMainForm calls InitFormTheme and it doesn't
-          have any of these controls. If it would be used: it works fully for buttons but for
-          radiobuttons and checkboxes it only updates the glyph and not the text color. }
+      const Control = ParentControl.Controls[I];
+      if Control is TButton then
         SetControlWindowTheme(Control as TWinControl, FormTheme.Dark);
-      end;
-
       if Control is TWinControl then
         InitWinControlTheme(Control as TWinControl);
     end;
@@ -158,16 +144,17 @@ procedure InitFormTheme(Form: TForm);
 begin
   if (Form = MainForm) or FormTheme.Dark then begin
     Form.Color := FormTheme.Colors[tcBack];
-  
+
     { Based on https://learn.microsoft.com/en-us/windows/apps/desktop/modernize/apply-windows-themes
       Unlike this article we check for Windows 10 Version 2004 because that's the first version
       that introduced DWMWA_USE_IMMERSIVE_DARK_MODE as 20 (the now documented value) instead of 19 }
     if WindowsVersionAtLeast(10, 0, 19041) then begin
+      Form.StyleElements := Form.StyleElements - [seBorder];
       const DWMWA_USE_IMMERSIVE_DARK_MODE = 20;
       var value: BOOL := FormTheme.Dark;
       DwmSetWindowAttribute(Form.Handle, DWMWA_USE_IMMERSIVE_DARK_MODE, @value, SizeOf(value));
     end;
-  
+
     InitWinControlTheme(Form);
   end;
 end;

Projects/Src/IDE.MainForm.dfm

@@ -14,6 +14,7 @@ object MainForm: TMainForm
   KeyPreview = True
   Menu = MainMenu1
   Position = poDefault
+  StyleElements = []
   OnAfterMonitorDpiChanged = FormAfterMonitorDpiChanged
   OnCloseQuery = FormCloseQuery
   OnKeyDown = FormKeyDown
@@ -47,6 +48,7 @@ object MainForm: TMainForm
       FullRepaint = False
       TabOrder = 1
       Visible = False
+      StyleName = 'Windows'
       OnMouseMove = SplitPanelMouseMove
     end
     object StatusPanel: TPanel
@@ -183,6 +185,7 @@ object MainForm: TMainForm
         Bevel = pbNone
         Width = 50
       end>
+    StyleName = 'Windows'
     OnClick = StatusBarClick
     OnDrawPanel = StatusBarDrawPanel
     OnResize = StatusBarResize
@@ -195,6 +198,7 @@ object MainForm: TMainForm
     Align = alTop
     BevelOuter = bvNone
     TabOrder = 0
+    StyleName = 'Windows'
     object ToolBar: TToolBar
       AlignWithMargins = True
       Left = 7

Projects/Src/IDE.MainForm.pas

@@ -680,7 +680,7 @@ var
 implementation
 
 uses
-  ActiveX, Clipbrd, ShellApi, ShlObj, IniFiles, Registry, Consts, Types, UITypes,
+  ActiveX, Clipbrd, ShellApi, ShlObj, IniFiles, Registry, Consts, Types, UITypes, Themes,
   Math, StrUtils, WideStrUtils, TypInfo,
   PathFunc, Shared.CommonFunc.Vcl, Shared.CommonFunc, Shared.FileClass, IDE.Messages, NewUxTheme.TmSchema, BrowseFunc,
   IDE.HtmlHelpFunc, TaskbarProgressFunc, IDE.ImagesModule,
@@ -6553,18 +6553,43 @@ begin
 end;
 
 procedure TMainForm.UpdateTheme;
+
+  procedure SetListBoxWindowTheme(const ListBox: TListBox);
+  begin
+    ListBox.Font.Color := FTheme.Colors[tcFore];
+    ListBox.Color := FTheme.Colors[tcBack];
+    ListBox.Invalidate;
+    SetControlWindowTheme(ListBox, FTheme.Dark);
+  end;
+
 begin
   FTheme.Typ := FOptions.ThemeType;
 
   SetHelpFileDark(FTheme.Dark);
 
+  { For MainForm the active style only impacts message boxes and tooltips: FMemos, Toolbar, SplitPanel, StatusBar
+    and the 4 ListBoxes ignore it because their StyleName property is set to 'Windows' always. Additionally,
+    for scrollbars and StatusBar, MainForm's StyleElements is empty. Menus ignore it because shMenus is removed
+    from TStyleManager.SystemHooks at startup. }
+  if FTheme.Dark then
+    TStyleManager.TrySetStyle('Windows11 Modern Dark')
+  else
+    TStyleManager.TrySetStyle('Windows');
+  { For some reason only MainForm needs this: with StyleName set to an empty string, dialog boxes look bad }
+  StyleName := TStyleManager.ActiveStyle.Name;
+
+  InitFormTheme(Self);
+
+  ToolbarPanel.Color := FTheme.Colors[tcToolBack];
+
   for var Memo in FMemos do begin
     Memo.UpdateThemeColorsAndStyleAttributes;
     SetControlWindowTheme(Memo, FTheme.Dark);
   end;
-
-  InitFormTheme(Self);
-  ToolbarPanel.Color := FTheme.Colors[tcToolBack];
+  SetListBoxWindowTheme(CompilerOutputList);
+  SetListBoxWindowTheme(DebugOutputList);
+  SetListBoxWindowTheme(DebugCallStackList);
+  SetListBoxWindowTheme(FindResultsList);
 
   if FTheme.Dark then begin
     ThemedToolbarVirtualImageList.ImageCollection := ImagesModule.DarkToolBarImageCollection;
@@ -7484,7 +7509,7 @@ end;
 { Should be removed if the main menu ever gets removed }
 procedure TMainForm.UAHDrawMenuBottomLine;
 begin
-  if FTheme.Dark then begin
+  if not (csDestroying in ComponentState) and (FTheme <> nil) and FTheme.Dark then begin
     var ClientRect: TRect;
     Windows.GetClientRect(Handle, ClientRect);
 		MapWindowPoints(Handle, 0, ClientRect, 2);

Projects/Src/IDE.OptionsForm.pas

@@ -82,6 +82,7 @@ uses
 procedure TOptionsForm.FormCreate(Sender: TObject);
 begin
   InitFormFont(Self);
+  InitFormTheme(Self);
 
   { Order must match CompFunc.TKeyMappingType }
   KeyMappingComboBox.Items.Add('Classic');

Projects/Src/IDE.StartupForm.pas

@@ -95,6 +95,7 @@ begin
   FResult := srNone;
 
   InitFormFont(Self);
+  InitFormTheme(Self);
 
   DonateImage.Hint := MainForm.UpdatePanelDonateImage.Hint;