https://github.com/dwyl/learn-to-send-email-via-google-script-html-no-server#how
부트스트랩 js 아래에 커스텀 js를 추가
<!-- Bootstrap script link -->
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0-alpha1/dist/js/bootstrap.bundle.min.js" integrity="sha384-w76AqPfDkMBDXo30jS1Sgez6pr3x5MlQ1ZAGC+nuZB+EYdgRZgiwxhTBTkF7CXvN" crossorigin="anonymous"></script>
<script data-cfasync="false" type="text/javascript" src="./js/form-submission-handler.js"></script>