To incorporate your React app into an existing container, you can specifically target the desired container for placement. For instance, if you wish to maintain the styles of the parent application, you can utilize ReactDOM to render your app within the body element.
ReactDOM.render(
<ActiveWidgetArea widgets={yourData}/>,
document.querySelector('body')
);
I experimented with this approach on a Drupal site and successfully displayed my React App within the designated container while preserving the surrounding elements. It is possible that any discrepancies observed were due to components loading after the React app's initiation. Alternatively, you can specify the html element as your target.
Understanding the structure of your parent application and the overall architecture of the website may provide additional insight and facilitate a smoother integration process.