And finaly add support for OS specific CSS.

Author: TurboGit

src/gui/gtk.c

@@ -3533,7 +3533,15 @@ void dt_gui_load_theme(const char *theme)
     _add_theme_import(&themecss, datadir, "themes", "condensed.css");
   }
 
-  // we could add OS specific css here if needed
+  // load any OS specific themes tweak file to fix some platform specific issues
+
+#ifdef __APPLE__
+  _add_theme_import(&themecss, datadir, "themes", "macos.css");
+#elif defined(_WIN32)
+  _add_theme_import(&themecss, datadir, "themes", "windows.css");
+#else
+  _add_theme_import(&themecss, datadir, "themes", "linux.css");
+#endif
 
   // and finally user.css