Lightbox

These modular elements can be readily used and customized in every layout across pages.

For more detail see, Glightbox Documentation

Stylesheet
<link href="assets/lib/lightbox2/css/lightbox.min.css" rel="stylesheet">
Javascript
<script src="assets/lib/lightbox2/js/lightbox.min.js"></script>
Example 
<a href="../assets/img/gallery/g7.jpg" data-gallery="gallery-2">
  <img class="img-fluid rounded" src="../assets/img/gallery/g7.jpg" alt="" />
</a>
<div class="row">
  <div class="col-sm-4 mb-4 mb-lg-0">
    <a href="../assets/img/gallery/g1.jpg" data-gallery="gallery-1">
      <img class="img-fluid rounded" src="../assets/img/gallery/g1.jpg" alt="" />
    </a>
  </div>
  <div class="col-sm-4 mb-4 mb-lg-0">
    <a class="post1" href="../assets/img/gallery/g2.jpg" data-gallery="gallery-1">
      <img class="img-fluid rounded" src="../assets/img/gallery/g2.jpg" alt="" />
    </a>
  </div>
  <div class="col-sm-4 mb-4 mb-lg-0">
    <a class="post1" href="../assets/img/gallery/g3.jpg" data-gallery="gallery-1">
      <img class="img-fluid rounded" src="../assets/img/gallery/g3.jpg" alt="" />
    </a>
  </div>
</div>