html,body {
    height: 100%;
}
body {
    background: url(../images/bg.jpg) center no-repeat;
    background-size: cover;
    overflow: hidden;
    padding:35px;
}
.row {
    justify-content: center;
    align-items: center;
    height: 100%;
    text-align: center;
}
img {
    display:block;
    margin:auto;
    max-width:100%;
}
.btn-main {
    display:block;
    max-width:330px;
    font-size:21px;
    padding: 15px;
    border-radius:10px;
    background:#000;
    color:#fff;
    margin: auto;
    margin-top:3rem;
    box-shadow:0px 0px 15px 0px rgb(113 221 211 / 0.4);
}

@media (min-width:768px) {
    .btn-main {
        margin-top:5rem;
    }
}