Learn how to create a modal image gallery (lightbox) with CSS and JavaScript:-This is a a slideshow of images where if you click a button then the button will popup the one image then after press next button the image will start slide

Simple Image Slider with Button

<style>
    .row > .column {
      padding: 0 8px;
    }
    .row:after {
      content: "";
      display: table;
      clear: both;
    }
    .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;
    }   
    .mySlides {
      display: none;
    }  
    .cursor {
      cursor: pointer;
    } 
    /* 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;
    }
    
    img {
      margin-bottom: -4px;
    }
    
    .caption-container {
      text-align: center;
      background-color: black;
      padding: 2px 16px;
      color: white;
    }
    
    .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);
    }
    </style>
    <!-- Change Your Title here -->
    <h2 style="text-align: center;">Image Gallery</h2>
    <div class="row">
    <!-- Change Your Button Tittle -->
    <div class="column"><button style="width: 100%;" onclick="openModal();currentSlide(1)" class="hover-shadow cursor">Image One</button></div>
    <div class="column"><button  style="width: 100%;" onclick="openModal();currentSlide(2)" class="hover-shadow cursor">Image two</button></div>
    <div class="column"><button style="width: 100%;" onclick="openModal();currentSlide(3)" class="hover-shadow cursor">Image three</button></div>
    <div class="column"><button style="width: 100%;" onclick="openModal();currentSlide(4)" class="hover-shadow cursor">Image four</button></div>
    </div>
    <div id="myModal" class="modal"><span class="close cursor" onclick="closeModal()">×</span>
    <div class="modal-content">
    <div class="mySlides">
    <!-- Change Your Image title Link -->
    <div class="numbertext">1 / 4</div>
    <img src="https://dev-authlabsupport.pantheonsite.io/wp-content/uploads/2019/12/banner-06.jpg" style="width: 100%;" /></div>
    <div class="mySlides">
    <!-- Change Your Image title Link -->
    <div class="numbertext">2 / 4</div>
    <img src="https://dev-authlabsupport.pantheonsite.io/wp-content/uploads/2019/12/banner-04.jpg" style="width: 100%;" /></div>
    <div class="mySlides">
    <!-- Change Your Image title Link -->
    <div class="numbertext">3 / 4</div>
    <img src="https://dev-authlabsupport.pantheonsite.io/wp-content/uploads/2019/12/banner-05.jpg" style="width: 100%;" /></div>
    <div class="mySlides">
    <!-- Change Your Image title Link -->
    <div class="numbertext">4 / 4</div>
    <img src="https://dev-authlabsupport.pantheonsite.io/wp-content/uploads/2019/12/home-new-bg-free-img.jpg" style="width: 100%;" /></div>
    <a class="prev" onclick="plusSlides(-1)">❮</a> <a class="next" onclick="plusSlides(1)">❯</a>
    <div class="caption-container">
    <p id="caption"></p>
    </div>
    <!-- Change Your Image title Link alt text to show bellow-->
    <div class="column"><img class="demo cursor" src="https://dev-authlabsupport.pantheonsite.io/wp-content/uploads/2019/12/banner-06.jpg" style="width: 100%;" onclick="currentSlide(1)" alt="Your Title of image 1" /></div>
    <div class="column"><img class="demo cursor" src="https://dev-authlabsupport.pantheonsite.io/wp-content/uploads/2019/12/banner-05.jpg" style="width: 100%;" onclick="currentSlide(2)" alt="Your Title of image 2" /></div>
    <div class="column"><img class="demo cursor" src="https://dev-authlabsupport.pantheonsite.io/wp-content/uploads/2019/12/banner-04.jpg" style="width: 100%;" onclick="currentSlide(3)" alt="Your Title of image 3" /></div>
    <div class="column"><img class="demo cursor" src="https://dev-authlabsupport.pantheonsite.io/wp-content/uploads/2019/12/home-new-bg-free-img.jpg" style="width: 100%;" onclick="currentSlide(4)" alt="Your Title of image 4" /></div>
    </div>
<!-- Change Your Image title Link -->
    </div>
    <script>
        /**
         * -------------------------------xxxxxxxxxxxx---------------------------------
         * Warning- if you use same class id then it will conflict with every slideshow
         * so please when you duplicate all the code then must change the class and id
         * -------------------------------xxxxxxxxxxxx---------------------------------
        */
    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;
    }
    </script>