[Winforms] Title bar theme follows system theme changes (#1595)

Author: godcop

webview/platforms/winforms.py

@@ -29,6 +29,7 @@
 from System.Drawing import Color, ColorTranslator, Icon, Point, Size, SizeF
 from System.Threading import ApartmentState, Thread, ThreadStart
 from System.Reflection import Assembly, BindingFlags
+from Microsoft.Win32 import SystemEvents
 
 kernel32 = ctypes.WinDLL('kernel32', use_last_error=True)
 logger = logging.getLogger('pywebview')
@@ -271,9 +272,41 @@ def __init__(self, window, cache_dir):
 
             self.localization = window.localization
 
+            self.update_title_bar_theme()
+            SystemEvents.UserPreferenceChanged += self.on_system_theme_changed
+
         def __str__(self):
             return f'<System.Windows.Forms object with {self.Handle} handle>'
 
+        def on_system_theme_changed(self, sender, e):
+            self.update_title_bar_theme()
+                
+        def update_title_bar_theme(self):
+            if self.is_dark_theme():
+                DwmSetWindowAttribute(self.Handle.ToInt32(), 20, 1)
+                DwmSetWindowAttribute(self.Handle.ToInt32(), 38, 2)
+            else:
+                DwmSetWindowAttribute(self.Handle.ToInt32(), 20, 0)
+                DwmSetWindowAttribute(self.Handle.ToInt32(), 38, 1)
+        
+        def is_dark_theme(self):
+            try:
+                personalize_key = winreg.OpenKey(
+                    winreg.HKEY_CURRENT_USER,
+                    r"Software\Microsoft\Windows\CurrentVersion\Themes\Personalize",
+                    0,
+                    winreg.KEY_READ
+                )
+                system_theme, _ = winreg.QueryValueEx(personalize_key, "SystemUsesLightTheme")
+                winreg.CloseKey(personalize_key)
+                if system_theme == 0:
+                    return True
+                else:
+                    return False
+            except Exception as e:
+                logger.error(f'Error while getting system theme: {e}')
+                return None
+
         def on_activated(self, *_):
             if not self.pywebview_window.focus:
                 windll.user32.SetWindowLongW(self.Handle.ToInt32(), -20, windll.user32.GetWindowLongW(self.Handle.ToInt32(), -20) | 0x8000000)