Fix QComboBox background and transparency workaround on macOS

Source/Core/DolphinQt/QtUtils/WrapInScrollArea.cpp

@@ -15,6 +15,7 @@ QWidget* GetWrappedWidget(QWidget* wrapped_widget, QWidget* to_resize, int margi
                           int margin_height)
 {
   auto* scroll = new QScrollArea;
+  scroll->setBackgroundRole(QPalette::PlaceholderText);
   scroll->setWidget(wrapped_widget);
   scroll->setWidgetResizable(true);
   scroll->setFrameStyle(QFrame::NoFrame);
@@ -30,18 +31,6 @@ QWidget* GetWrappedWidget(QWidget* wrapped_widget, QWidget* to_resize, int margi
                       std::max(recommended_height, to_resize->height()));
   }
 
-#if defined(_WIN32) || defined(__APPLE__)
-  // Transparency can cause unwanted side-effects on OSes other than Windows / macOS
-
-  // Make sure the background color stays consistent with the parent widget
-  QPalette p = wrapped_widget->palette();
-
-  p.setColor(QPalette::Window, QColor(0, 0, 0, 0));
-
-  wrapped_widget->setPalette(p);
-  scroll->setPalette(p);
-#endif
-
   return scroll;
 }