bootstrap 4 - carousel, img-fluid
portrait images and landscape images
by Glynne Turner
HTML
<script src="//code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<link rel="stylesheet" href="//stackpath.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css">
<script src="//cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.0/umd/popper.min.js"></script>
<script src="//stackpath.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css">
<div id="carouselExampleControls" class="carousel slide" data-ride="carousel">
<div class="carousel-inner">
<div class="carousel-item active">
<img class="img-fluid" src="https://images.pexels.com/photos/132037/pexels-photo-132037.jpeg" alt="First slide">
</div>
<div class="carousel-item">
<img class="img-fluid" src="https://thumbs.dreamstime.com/b/dead-tree-tall-portrait-view-blue-sky-background-57002950.jpg" alt="Second slide">
</div>
<div class="carousel-item">
<img class="img-fluid" src="https://images.pexels.com/photos/414171/pexels-photo-414171.jpeg" alt="Third slide">
</div>
</div>
<a class="carousel-control-prev" href="#carouselExampleControls" role="button" data-slide="prev">
<span class="carousel-control-prev-icon" aria-hidden="true"></span>
<span class="sr-only">Previous</span>
</a>
<a class="carousel-control-next" href="#carouselExampleControls" role="button" data-slide="next">
<span class="carousel-control-next-icon" aria-hidden="true"></span>
<span class="sr-only">Next</span>
</a>
</div>
CSS
img{max-width:100vw !important; max-height:100vh !important; margin:auto}
.carousel-item{background:pink; text-align:center}