egui_demo_app: don't do a transparent native window

It doesn't work great on Mac

egui_demo_app/src/main.rs

@@ -8,8 +8,6 @@ fn main() {
     tracing_subscriber::fmt::init();
 
     let options = eframe::NativeOptions {
-        // Let's show off that we support transparent windows
-        transparent: true,
         drag_and_drop_support: true,
         ..Default::default()
     };

egui_demo_lib/src/demo/demo_app_windows.rs

@@ -201,17 +201,7 @@ impl DemoWindows {
             show_menu_bar(ui);
         });
 
-        {
+        egui::CentralPanel::default().show(ctx, |_ui| {}); // just to paint a background for the windows to be on top of. Needed on web because of https://github.com/emilk/egui/issues/1548
-            let mut fill = ctx.style().visuals.extreme_bg_color;
-            if !cfg!(target_arch = "wasm32") {
-                // Native: WrapApp uses a transparent window, so let's show that off:
-                // NOTE: the OS compositor assumes "normal" blending, so we need to hack it:
-                let [r, g, b, _] = fill.to_array();
-                fill = egui::Color32::from_rgba_premultiplied(r, g, b, 180);
-            }
-            let frame = egui::Frame::none().fill(fill);
-            egui::CentralPanel::default().frame(frame).show(ctx, |_| {});
-        }
 
         self.windows(ctx);
     }