Create a guestbook with JavaScript

<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/css/bootstrap.min.css" rel="stylesheet"
      integrity="sha384-EVSTQN3/azprG1Anm3QDgpJLIm9Nao0Yz1ztcQTwFspd3yD65VohhpuuCOmLASjC" crossorigin="anonymous">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.2/dist/js/bootstrap.bundle.min.js"
        integrity="sha384-MrcW6ZMFYlzcLA8Nl+NtUVF0sA7MsXsP1UyJoMp4YLEuNSfAP+JcXn/tWtIaxVXM"
        crossorigin="anonymous"></script>

<title>초미니홈피 - 팬명록</title>

<link href="https://fonts.googleapis.com/css2?family=Noto+Serif+KR:wght@200;300;400;500;600;700;900&display=swap"
      rel="stylesheet">
<style>
    * {
        font-family: 'Noto Serif KR', serif;
    }

    .mypic {
        width: 100%;
        height: 300px;

        background-image: linear-gradient(0deg, rgba(0, 0, 0, 0.5), rgba(0, 0, 0, 0.5)), url('https://w.namu.la/s/cbd0db41dbd4d4d9e445ae45d775bf038f17ccd52d28d7a4078bcdbf8b3e3e590165809f199d95f0b2514838b5a61a95eeca4e86a3907989bf32fbc1dcb619d6d26d4ee5da947b79bbb57cb3e0b2f4f11dfc1b80d7620cc1fd5087f31f76acb6');
        background-position: center 30%;
        background-size: cover;

        color: white;

        display: flex;
        flex-direction: column;
        align-items: center;
        justify-content: center;
    }

    .mypost {
        width: 95%;
        max-width: 500px;
        margin: 20px auto 20px auto;

        box-shadow: 0px 0px 3px 0px black;
        padding: 20px;
    }

    .mypost > button {
        margin-top: 15px;
    }

    .mycards {
        width: 95%;
        max-width: 500px;
        margin: auto;
    }

    .mycards > .card {
        margin-top: 10px;
        margin-bottom: 10px;
    }
</style>