html, body {
    margin: 20;
    padding: 20;
    width: 100%;
    height: 100%;
    background-color: #ffffff;
}

body {
    display: flex;
    justify-content: center; /* horizontal centering */
    align-items: center;     /* vertical centering */
}

img {
    width: 500px;
    height: 500px;
    display: block;
}