<!-- Start of Banner -->
* {box-sizing: border-box;}
body {font-family: Verdana, sans-serif;   background-color: #0C71C3;}
.mySlides {display: none;}
img {vertical-align: middle;}

/* Slideshow container */
.slideshow-container {
   /* max-width: 100%; */
  width:900px;
  height:300px;
  position: relative;
  margin: auto;
}

/* Caption text */
.text {
  color: #f2f2f2;
  font-size: 15px;
  padding: 8px 12px;
  position: absolute;
  bottom: 8px;
  width: 100%;
  text-align: center;
}

/* Number text (1/3 etc) */
.numbertext {
  color: #f2f2f2;
  font-size: 12px;
  padding: 8px 12px;
  position: absolute;
  top: 0;
}

/* The dots/bullets/indicators */
.dot {
  height: 15px;
  width: 15px;
  height: 0px;
  width: 0px;
  margin: 0 2px;
  background-color: #bbb;
  border-radius: 50%;
  display: inline-block;
  transition: background-color 0.6s ease;
}

.active {
  background-color: #717171;
}

/* Fading animation */
.fade {
  animation-name: fade;
  animation-duration: 1.5s;
}

@keyframes fade {
  from {opacity: .4} 
  to {opacity: 1}
}

/* On smaller screens, decrease text size */
@media only screen and (max-width: 300px) {
  .text {font-size: 11px}
}
<!-- End of Banner -->

<!-- start of main content CSS-->

div.mycontainer {
  width:900px;
  vertical-align: top;
  text-align:center;
}
div.col1{
  width:600px;
   vertical-align: top;
  text-align: left;
  display: inline-block; 
}
div.col2{
  width:300px;
  vertical-align: top;
  text-align: left;
  display: inline-block; 
}
div.fullcolumn{
  width:900px;
  display: inline-block; 
}
/* this can be used as a back button */
.bigbluebutton {padding:10px;margin:5px;background-color: #ffffff;
width:290px;}
.bigbluebutton span {color:#0C71C3; font-family: 'Tiro Devanagari Hindi', serif; font-size:20pt; font-style: italic; font-weight:bold;}

body {
  background-color: #0C71C3;
}

h1 {color:#ffffff; font-family: 'Tiro Devanagari Hindi', serif; font-size:30pt; font-style: italic;}
h2 {color:#ffffff; font-family: 'Tiro Devanagari Hindi', serif; font-size:25pt; font-style: italic;}
p {color:#ffffff; font-size:12pt; font-family: 'Noto Sans', sans-serif;}
li {color:#ffffff; font-size:12pt; font-family: 'Noto Sans', sans-serif;}

<!-- end of main content CSS-->

<!-- start of menu CSS-->
#myImg {
  border-radius: 5px;
  cursor: pointer;
  transition: 0.3s;
}

#myImg:hover {opacity: 0.7;}

/* The Modal (background) */
.modal {
  display: none; /* Hidden by default */
  position: fixed; /* Stay in place */
  z-index: 1; /* Sit on top */
  padding-top: 100px; /* Location of the box */
  left: 0;
  top: 0;
  width: 100%; /* Full width */
  height: 100%; /* Full height */
  overflow: auto; /* Enable scroll if needed */
  background-color: rgb(0,0,0); /* Fallback color */
  background-color: rgba(0,0,0,0.9); /* Black w/ opacity */
}

/* Modal Content (image) */
.modal-content {
  margin: auto;
  display: block;
  width: 80%;
  max-width: 700px;
}

/* Caption of Modal Image */
#caption {
  margin: auto;
  display: block;
  width: 80%;
  max-width: 700px;
  text-align: center;
  color: #ccc;
  padding: 10px 0;
  height: 150px;
}

/* Add Animation */
.modal-content, #caption {  
  -webkit-animation-name: zoom;
  -webkit-animation-duration: 0.6s;
  animation-name: zoom;
  animation-duration: 0.6s;
}

@-webkit-keyframes zoom {
  from {-webkit-transform:scale(0)} 
  to {-webkit-transform:scale(1)}
}

@keyframes zoom {
  from {transform:scale(0)} 
  to {transform:scale(1)}
}

/* The Close Button */
.close {
  position: absolute;
  top: 15px;
  right: 35px;
  color: #f1f1f1;
  font-size: 40px;
  font-weight: bold;
  transition: 0.3s;
}

.close:hover,
.close:focus {
  color: #bbb;
  text-decoration: none;
  cursor: pointer;
}

/* 100% Image Width on Smaller Screens */
@media only screen and (max-width: 700px){
  .modal-content {
    width: 100%;
  }
}
<!-- end of menu CSS-->

<!-- Start of java script for  Banner -->
<script>
let slideIndex = 0;
showSlides();

function showSlides() {
  let i;
  let slides = document.getElementsByClassName("mySlides");
  let dots = document.getElementsByClassName("dot");
  for (i = 0; i < slides.length; i++) {
    slides[i].style.display = "none";  
  }
  slideIndex++;
  if (slideIndex > slides.length) {slideIndex = 1}    
  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";
  setTimeout(showSlides, 2000); // Change image every 2 seconds
}
<!-- End of java script for  Banner -->

// Get the modal
var modal = document.getElementById("myModal");

// Get the image and insert it inside the modal - use its "alt" text as a caption
var img = document.getElementById("myImg");
var modalImg = document.getElementById("img01");
var captionText = document.getElementById("caption");
img.onclick = function(){
  modal.style.display = "block";
  modalImg.src = this.src;
  captionText.innerHTML = this.alt;
}

// Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];

// When the user clicks on <span> (x), close the modal
span.onclick = function() { 
  modal.style.display = "none";
}
</script>
</body>
</html>