### Preflight Checklist

- [X] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/main/CONTRIBUTING.md) for this project.
- [X] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/main/CODE_OF_CONDUCT.md) that this project adheres to.
- [X] I have searched the [issue tracker](https://www.github.com/electron/electron/issues) for a feature request that matches the one I want to file, without success.

### Electron Version

14.0.1

### What operating system are you using?

macOS

### Operating System Version

macOS Big Sur 11.6.1

### What arch are you using?

x64

### Last Known Working Electron version

14.0.0

### Expected Behavior


When `BrowserView.setBackgroundColor` is called with an explicit color, expect the background to be the color selected.

When `BrowserView.setBackgroundColor` is not called, expect the background of the `BrowserView` to be transparent by default; and can see through `BrowserWindow`'s background color.



### Actual Behavior

The `BrowserView` background is always white.

### Testcase Gist URL

https://gist.github.com/kevinlinv/2de60478ffec6a2f18f1ec0fc6f5add9

### Additional Information

Here is a quick recording that reproduces the error.

https://user-images.githubusercontent.com/44967897/140694174-e27aff28-1847-4813-bc46-d9fda6569128.mp4


shell/browser/api/electron_api_web_contents.cc
auto* const host = ontents()->GetMainFrame();
  if (host)
    host->CopyImageAt(x, y);
}
void WebContents::Focus() {
   Focusing on WebContents does not automatically focus the window on macOS
   and Linux, do it manually to match the behavior on Windows.
#if defined(OS_MAC) || defined(OS_LINUX)
  if (owner_window())
    owner_window()->Focus(true);
#endif
  ontents()->Focus();
}
#if !defined(OS_MAC)
bool WebContents::IsFocused() const {
  auto* view = ontents()->GetRenderWidgetHostView();
  if (!view)
    return false;
  if (GetType() != Type::kBackgroundPage) {
    auto* window = ontents()->GetNativeView()->GetToplevelWindow();
    if (window && !window->IsVisible())
      return false;
  }
  return view->HasFocus();
}
#endif
void WebContents::SendInputEvent(v8::Isolate* isolate,