function _IsThemeActive: Boolean;
// Returns True if the user uses XP style
const
 themelib = 'uxtheme.dll';
type
 TIsThemeActive = function: BOOL; stdcall;
var
 IsThemeActive: TIsThemeActive;
 huxtheme: HINST;
begin
 Result := False;
 // Check if XP or later Version
 if (Win32Platform = VER_PLATFORM_WIN32_NT) and
  (((Win32MajorVersion = 5) and (Win32MinorVersion >= 1)) or
  (Win32MajorVersion > 5)) then
 begin
  huxtheme := LoadLibrary(themelib);
  if huxtheme <> 0 then
  begin
  try
  IsThemeActive := GetProcAddress(huxtheme, 'IsThemeActive');
  Result := IsThemeActive;
  finally
  if huxtheme > 0 then
  FreeLibrary(huxtheme);
  end;
  end;
 end;
end;
// Example Call:
procedure TForm1.Button1Click(Sender: TObject);
begin
 if _IsThemeActive then
  ShowMessage('Windows Themes are active.');
end;

uses
Themes;
...
if ThemeServices.ThemesEnabled then // Тема использется