.center {
    margin: 0;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    max-width: 50%;
    max-height: 50%;
}

img.center {
    width: auto;
    height: auto;
    max-width: 100%;
    max-height: 100%;
    margin: 0;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    box-sizing: border-box;
    padding: 16px;
}