### 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
v8::Isolate* isolate = JavascriptEnvironment::GetIsolate();
  gin_helper::Promise<v8::Local<v8::Value>> promise(isolate);
  v8::Local<v8::Promise> handle = promise.GetHandle();
  PrintPreviewMessageHandler::FromWebContents(ontents())
      ->PrintToPDF(std::move(settings), std::move(promise));
  return handle;
}
#endif
void WebContents::AddWorkSpace(gin::Arguments* args,
                               const base::FilePath& path) {
  if (path.empty()) {
    gin_helper::ErrorThrower(args->isolate())
        .ThrowError("path cannot be empty");
    return;
  }
  DevToolsAddFileSystem(std::string(), path);
}
void WebContents::RemoveWorkSpace(gin::Arguments* args,
                                  const base::FilePath& path) {
  if (path.empty()) {
    gin_helper::ErrorThrower(args->isolate())
        .ThrowError("path cannot be empty");
    return;
  }
  DevToolsRemoveFileSystem(path);
}
void WebContents::Undo() {
  ontents()->Undo();
}
void WebContents::Redo() {