body {
    background: no-repeat url("/static/images/serrure.jpg");
    background-size: cover;
    background-color: #f8ebc9;
    margin-left: 3vw;
    margin-top: 5vh;
}
body .main {
    margin: auto;
    display: flex;
    flex-direction: column;
    position: absolute;
    top: 50%;
    left: 41%;
    transform: translate(-100%, -50%);
    opacity: 80%;
    max-width: 30%;
}

@media screen and (max-width: 900px) {
    body .main {
	left: 50%;
	transform: translate(-50%, -50%);
	max-width: 50%;
  }
}