모달창 뒤 스크롤 막기

useEffect(() => {
  document.body.style.cssText = `
    position: fixed; 
    top: -${window.scrollY}px;
    overflow-y: scroll;
    width: 100%;`;
  return () => {
    const scrollY = document.body.style.top;
    document.body.style.cssText = '';
    window.scrollTo(0, parseInt(scrollY || '0', 10) * -1);
  };
}, []);

출처 : https://velog.io/@do_dadu/React%EC%97%90%EC%84%9C-Modal-%EA%B5%AC%ED%98%84%ED%95%98%EA%B8%B0feat.-createPortal-%EC%8A%A4%ED%81%AC%EB%A1%A4-%EB%A7%89%EA%B8%B0