html,
body {
    height: 100vh;
    background-color: #333;
}

body {
    display: -ms-flexbox;
    display: -webkit-box;
    display: flex;
    -ms-flex-pack: center;
    -webkit-box-pack: center;
    justify-content: center;
    color: #fff;
    text-shadow: 0 .05rem .1rem rgba(0, 0, 0, .5);
    box-shadow: inset 0 0 5rem rgba(0, 0, 0, .5);
}

.gallery-slot {
    background-color: #555555;
    box-shadow: 0 0 2rem rgba(0, 0, 0, .5);
}