style.css

html, body {
    height: 100%; 
}
body {
    margin: 0;
    padding: 0;
    background-color: #00DBDE;
    background-image: linear-gradient(138deg, #00DBDE 0%, #FC00FF 100%);
    background-size: cover;
    background-repeat: no-repeat;
    background-attachment: fixed;
    width: 100vw;
}

.header {
    color: white;
    display: flex;
    justify-content: center;
    align-items: center;
    width: 100vw;
    height: 55px;
}

.card {
    width: 90vw;
    max-width: 480px;
    margin: 0 auto;
    border-radius: 5px;
    background-color: rgba(255, 255, 255, 1);
}

.modal {
    left: 50%;
    transform: translateX(-50%);
    width: 480px;
    overflow: hidden;
    position: relative;
}

.modal img {
    max-width: 100%;
}

.submitImg {
    margin-top: 20px;
    width: 100px;
    left: 50%;
    transform: translateX(-50%);
    position: relative;
}

#main {
    display: flex;
    justify-content: center;
    align-items: center;
}

canvas {
    background-color: white;
}

#preview {
    /* object-fit: scale-down; */
    width: 100%;
    height: 100%;
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 480px;
    height: 480px;
    overflow: hidden;
    margin-top: 50px;
    margin-bottom: 50px;
}

@media(max-width: 600px) {
    #preview {
        width: 80vw;
        height: 80vw;
    }
    .form-control {
        width: 80vw;
    }
    .modal {
        width: 80vw;
    }
}