#outerholder {
    max-width: 600px;
}


#imgholder img {
    position: absolute;
    width: auto;
    max-width: 100%;
    max-height: 100%;
    margin: auto;
    left: 0;
    right: 0;
    top: 0;
    bottom: 0;
}

.trans {
    opacity: 0;
    filter:  brightness(3);
    transition: 1.5s linear;
}

.vis {
    opacity: 1;
    filter:  brightness(1);
    transition: 1.5s linear;
}