import ReactFloatingScroll from 'path/to/ReactFloatingScroll';
import LongContentComponent from 'path/to/LongContentComponent';
...

class YourParentComponent extends Component {

constructor(props) {
    super(props);

    this.contentRef = React.createRef();
    ...
    }

...

render() {
    return (
        <ReactFloatingScroll contentRef={this.contentRef}
                      innerScrollableClass={`${innerScrollableClassName}`}>
            <LongContentComponent {...props}
                ref={this.contentRef}>
        </ReactFloatingScroll>);
    }
}