Lightbox gallery

<div class="row">
<div class="col-lg-3 col-md-4 col-sm-6 portfolio-item">
<div class="card h-100">
<a href="#"><img src="http://www.tillmann-verpackungen.com/wp-content/uploads/2017/12/tillmann-verpackungen-referenz-esd-tray-luft-raumfahrt.jpg" onmouseover="this.src='http://www.tillmann-verpackungen.com/wp-content/uploads/2017/12/oeca3.jpg'" onmouseout="this.src='http://www.tillmann-verpackungen.com/wp-content/uploads/2017/12/tillmann-verpackungen-referenz-esd-tray-luft-raumfahrt.jpg'" class="card-img-top" onclick="openModal();currentSlide(1)"></a>
<div id="myModal" class="modal">
<span class="close cursor" onclick="closeModal()">&times;</span>
<div class="modal-content">

<div class="mySlides">
<div class="numbertext">1 / 4</div>
<img src="http://placehold.it/700x400" style="width:60%;">
</div>

<div class="mySlides">
<div class="numbertext">2 / 4</div>
<img src="http://www.tillmann-verpackungen.com/wp-content/uploads/2017/12/oeca1.jpg" style="width:60%">
</div>

<div class="mySlides">
<div class="numbertext">3 / 4</div>
<img src="http://www.tillmann-verpackungen.com/wp-content/uploads/2017/12/oeca6.jpg" style="width:60%">
</div>

<div class="mySlides">
<div class="numbertext">4 / 4</div>
<img src="http://www.tillmann-verpackungen.com/wp-content/uploads/2017/12/oeca5.jpg" style="width:60%">
</div>

<a class="prev" onclick="plusSlides(-1)">&#10094;</a>
<a class="next" onclick="plusSlides(1)">&#10095;</a>

<div class="caption-container">
<p id="caption"></p>
</div>


<div class="column">
<img class="demo cursor" src="http://www.tillmann-verpackungen.com/wp-content/uploads/2017/12/oeca3.jpg" style="width:60%" onclick="currentSlide(1)" alt="Nature and sunrise">
</div>
<div class="column">
<img class="demo cursor" src="http://www.tillmann-verpackungen.com/wp-content/uploads/2017/12/oeca1.jpg" style="width:60%" onclick="currentSlide(2)" alt="Trolltunga, Norway">
</div>
<div class="column">
<img class="demo cursor" src="http://www.tillmann-verpackungen.com/wp-content/uploads/2017/12/oeca5.jpg" style="width:60%" onclick="currentSlide(3)" alt="Mountains and fjords">
</div>
<div class="column">
<img class="demo cursor" src="http://www.tillmann-verpackungen.com/wp-content/uploads/2017/12/oeca5.jpg" style="width:60%" onclick="currentSlide(4)" alt="Northern Lights">
</div>
</div>
</div>


<script>
function openModal() {
document.getElementById('myModal').style.display = "block";
}

function closeModal() {
document.getElementById('myModal').style.display = "none";
}

var slideIndex = 1;
showSlides(slideIndex);

function plusSlides(n) {
showSlides(slideIndex += n);
}

function currentSlide(n) {
showSlides(slideIndex = n);
}

function showSlides(n) {
var i;
var slides = document.getElementsByClassName("mySlides");
var dots = document.getElementsByClassName("demo");
var captionText = document.getElementById("caption");
if (n > slides.length) {slideIndex = 1}
if (n < 1) {slideIndex = slides.length}
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
for (i = 0; i < dots.length; i++) {
dots[i].className = dots[i].className.replace(" active", "");
}
slides[slideIndex-1].style.display = "block";
dots[slideIndex-1].className += " active";
captionText.innerHTML = dots[slideIndex-1].alt;
}


.row > .column {
  padding: 0 8px;
}
.row:after {
  content: "";
  display: table;
  clear: both;
}

/* Create four equal columns that floats next to eachother */
.column {
  float: left;
  width: 25%;
}
/* The Modal (background) */
.modal {
  display: none;
  position: fixed;
  z-index: 1;
  padding-top: 100px;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  overflow: auto;
  background-color: black;
}

/* Modal Content */
.modal-content {
  position: relative;
  background-color: #fefefe;
  margin: auto;
  padding: 0;
  width: 90%;
  max-width: 1200px;
}
/* The Close Button */
.close {
  color: white;
  position: absolute;
  top: 10px;
  right: 25px;
  font-size: 35px;
  font-weight: bold;
}
.close:hover,
.close:focus {
  color: #999;
  text-decoration: none;
  cursor: pointer;
}

/* Hide the slides by default */
.mySlides {
  display: none;
}
/* Next & previous buttons */
.prev,
.next {
  cursor: pointer;
  position: absolute;
  top: 50%;
  width: auto;
  padding: 16px;
  margin-top: -50px;
  color: white;
  font-weight: bold;
  font-size: 20px;
  transition: 0.6s ease;
  border-radius: 0 3px 3px 0;
  user-select: none;
  -webkit-user-select: none;
}
/* Position the "next button" to the right */
.next {
  right: 0;
  border-radius: 3px 0 0 3px;
}
/* On hover, add a black background color with a little bit see-through */
.prev:hover,
.next:hover {
  background-color: rgba(0, 0, 0, 0.8);
}

/* Number text (1/3 etc) */
.numbertext {
  color: #f2f2f2;
  font-size: 12px;
  padding: 8px 12px;
  position: absolute;
  top: 0;
}

/* Caption text */
.caption-container {
  text-align: center;
  background-color: black;
  padding: 2px 16px;
  color: white;
}
img.demo {
  opacity: 0.6;
}
.active,
.demo:hover {
  opacity: 1;
}
img.hover-shadow {
  transition: 0.3s
}

.hover-shadow:hover {
  box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19)
}

/*!
* Start Bootstrap - 4 Col Portfolio (https://startbootstrap.com/template-overviews/4-col-portfolio)
* Copyright 2013-2017 Start Bootstrap
* Licensed under MIT (https://github.com/BlackrockDigital/startbootstrap-4-col-portfolio/blob/master/LICENSE)
*/

body {
padding-top: 54px;
}

@media (min-width: 992px) {
body {
padding-top: 56px;
}
}

.portfolio-item {
margin-bottom: 30px;
}

.pagination {
margin-bottom: 30px;
}
.row > .column {
padding: 0 8px;
}

.row:after {
content: "";
display: table;
clear: both;
}

/* Create four equal columns that floats next to eachother */
.column {
float: left;
width: 25%;
}

/* The Modal (background) */
.modal {
display: none;
position: fixed;
z-index: 1;
padding-top: 50px;
left: 0;
top: 0;
width: 100%;
height: 100%;
overflow: auto;
background-color: black;
}

/* Modal Content */
.modal-content {
position: relative;
background-color: #fefefe;
margin: auto;
padding: 0;
width: 90%;
max-width: 1200px;
}

/* The Close Button */
.close {
color: white;
position: absolute;
top: 10px;
right: 25px;
font-size: 35px;
font-weight: bold;
}

.close:hover,
.close:focus {
color: #999;
text-decoration: none;
cursor: pointer;
}

/* Hide the slides by default */
.mySlides {
display: none;
width:100%;
background:black;
}

.myslides img{
width:100%;
height:auto;
}

/* Next & previous buttons */
.prev,
.next {
cursor: pointer;
position: absolute;
top: 50%;
width: auto;
padding: 16px;
margin-top: -50px;
color: white;
font-weight: bold;
font-size: 20px;
transition: 0.6s ease;
border-radius: 0 3px 3px 0;
user-select: none;
-webkit-user-select: none;
}

/* Position the "next button" to the right */
.next {
right: 0;
border-radius: 3px 0 0 3px;
}

/* On hover, add a black background color with a little bit see-through */
.prev:hover,
.next:hover {
background-color: rgba(0, 0, 0, 0.8);
}

/* Number text (1/3 etc) */
.numbertext {
color: #f2f2f2;
font-size: 12px;
padding: 8px 12px;
position: absolute;
top: 0;
}

/* Caption text */
.caption-container {
text-align: center;
background-color: black;
padding: 2px 16px;
color: white;
}

img.demo {
opacity: 0.6;
}

.active,
.demo:hover {
opacity: 1;
}

img.hover-shadow {
transition: 0.3s
}

.hover-shadow:hover {
box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19)
}