html {
    font-size: 60px;
    color: yellow;
    text-decoration: underline;
}

body {
    background-image: url(/images/12-indispensables-deco-pour-un-Noel-de-reve.jpg);
}

div {
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
}

img {
    width: 350px;
}

button {
    display: block;
    margin-left: auto;
    margin-right: auto;
}