.fotogalerij {
    text-align: center;
    width: 420px;
    max-width: 100%;
    margin: 10px auto;
}

.fotogalerij img {
    border: 2px solid darkgrey;
    /*margin: 4px;*/
}
    
.foto-popup {
    display: none;
}
.foto-popup:target {
    display: block;
    position: fixed;
    z-index: 999;
    width: 100%;
    height: 100%;
    text-align: center;
    top: 0;
    left: 0;
    right: 0;
    background: rgba(0,0,0,0.8);
    max-width: none;
}

  .foto-popup img {
    max-width: 90%;
    position: relative;
    top: 50%;
    transform: translateY(-50%);  
}


.vorige, .volgende {
    position: fixed;
    top: 50%;
    transform: translateY(-50%);  
    text-decoration: none;
    color: darkgrey;
    font-size: 5em;
}

.vorige:hover, .volgende:hover {
    color: white;
}
.vorige {
    left: 20px;
}

.volgende {
    right: 20px;
}

@media screen and (max-width: 800px) {
    .vorige, .volgende { font-size: 3em; }
}