Unable to scroll vertically in modal in React

I'm trying to show modal in my React Project. I set the overflow of body to hidden through useEffect when the modal is showing (otherwise, it shows the scrollbar of main page's content beneath modal). And it prvents scrolling of background content perfectly but the issue is that I'm unable to scroll in my modal as well.
Here is the code of main page:

import React, { useState } from "react";
import { render } from "react-dom";
import MyModal from "./MyModal";
import "./index.css";

function App() {
  const [showModal, setShowModal] = useState(false);
  return (
    <div className="wrapper">
      <button
        onClick={() => {
          setShowModal((current) => !current);
        }}
      >
        {`${showModal ? "Hide Modal" : "Show Modal"}`}
      </button>
      {showModal && <MyModal {...{ showModal, setShowModal }} />}
      <p>
        Lorem Ipsum is simply dummy text of the printing and typesetting
        industry. Lorem Ipsum has been the industry's standard dummy text ever
        since the 1500s, when an unknown printer took a galley of type and
        scrambled it to make a type specimen book. It has survived not only five
        centuries, but also the leap into electronic typesetting, remaining
        essentially unchanged. It was popularised in the 1960s with the release
        of Letraset sheets containing Lorem Ipsum passages, and more recently
        with desktop publishing software like Aldus PageMaker including versions
        of Lorem Ipsum.
      </p>
      
    </div>
  );
}

render(<App />, document.getElementById("root"));

And this is the code for modal:

import { useEffect } from "react";
import "./modal.css";

const MyModal = ({ showModal, setShowModal }) => {
  useEffect(() => {
    document.body.style.overflowY = "hidden";
    return () => {
      document.body.style.overflowY = "auto";
    };
  }, []);
  return (
    <div className="modal-background">
      <button
        onClick={() => {
          setShowModal(false);
        }}
      >
        Close
      </button>
      <p className="heading">This is Modal</p>
      <p>
        Lorem Ipsum is simply dummy text of the printing and typesetting
        industry. Lorem Ipsum has been the industry's standard dummy text ever
        since the 1500s, when an unknown printer took a galley of type and
      </p>
    </div>
  );
};

export default MyModal;

And here is the codesandbox live example: https://codesandbox.io/s/lockingmodal-8mvn36?file=/index.js:1160-4493

add these two lines to your class "modal-background"

height:50vh;
overflow:auto;