Creating a Slider / Carousel with CSS Flexbox (with infinite repeating items in loop)

We can create an infinitely scrolling slider using CSS Flexbox with the help of JavaScript.
The following examples illustrate carousel using CSS.
 Live Demo
<!DOCTYPE html>
<html>
   <head>
      <style>
         img {
            width: 100%;
         }
         .container {
            max-width: 600px;
            position: relative;
            margin: 6% auto;
         }
         .prevbtn, .nextbtn {
            position: absolute;
            top: 50%;
            padding: 12px;
            margin-top: -20px;
            color: white;
            font-weight: bold;
            cursor: pointer;
            transition: 0.2s ease-in;
            border-radius: 50%;
         }
         .prevbtn:hover, .nextbtn:hover {
            background-color: darkgrey;
            color: rgb(0,0,0);
         }
         .nextbtn {
            right: 0;
         }
      </style>
   </head>
   <body>
      <div class="container">
         <div class="slide">
            <img src="https://images.unsplash.com/photo-1609517904792-bac493d55556?crop=entropy&cs=tinysrgb&fit=crop&fm=jpg&h=200&ixlib=rb-1.2.1&q=80&w=700" />
         </div>
         <div class="slide">
            <img src="https://images.unsplash.com/photo-1609883475382-c4c9378569e5?crop=entropy&cs=tinysrgb&fit=crop&fm=jpg&h=200&ixlib=rb-1.2.1&q=80&w=700" />
         </div>
         <div class="slide">
            <img src="https://images.unsplash.com/photo-1610258648552-fe6407d664a1?crop=entropy&cs=tinysrgb&fit=crop&fm=jpg&h=200&ixlib=rb-1.2.1&q=80&w=700" />
         </div>
         <div class="slide">
            <img src="https://images.unsplash.com/photo-1610258648552-fe6407d664a1?crop=entropy&cs=tinysrgb&fit=crop&fm=jpg&h=200&ixlib=rb-1.2.1&q=80&w=700" />
         </div>
         <div class="slide">
            <img src="https://images.unsplash.com/photo-1611094607507-8c8173e5cf33?crop=entropy&cs=tinysrgb&fit=crop&fm=jpg&h=200&ixlib=rb-1.2.1&q=80&w=700" />
         </div>
         <a class="prevbtn" onclick="changeSlide(-1)">❮</a>
         <a class="nextbtn" onclick="changeSlide(1)">❯</a>
      </div>
      <script>
         let slideIndex = [1,1];
         viewSlides(1);
         function changeSlide(n) {
            viewSlides(slideIndex[0] += n);
         }
         function viewSlides(n) {
            let ele = document.getElementsByClassName("slide");
            if (n > ele.length) {
               slideIndex[0] = 1
            }
            if (n < 1) {
               slideIndex[0] = ele.length
            }
            for (i = 0; i < ele.length; i++) {
               ele[i].style.display = "none";
            }
            ele[slideIndex[0]-1].style.display = "block";
         }
      </script>
   </body>
</html>
This gives the following output
 Live Demo
<!DOCTYPE html>
<html>
   <head>
      <style>
         .container {
            height: 120px;
            max-width: 600px;
            margin: 12px auto;
            position: relative;
            overflow: hidden;
            transform: translate3d(0, 0, 0);
            border: 4px ridge rgba(20,30,240,0.6);
         }
         .container > div {
            height: 120px;
            width: 2400px;
            background: url(https://images.unsplash.com/photo-1611485916153-fce531587fe0?crop=entropy&cs=tinysrgb&fit=crop&fm=jpg&h=120&ixlib=rb-1.2.1&q=80&w=120);
            position: absolute;
            height: 100%;
            transform: translate3d(0, 0, 0);
         }
         .container .slider {
            animation: slideshow 20s linear infinite;
         }
         @keyframes slideshow {
            100% {
               transform: translateX(-33.33%);
            }
         }
      </style>
   </head>
   <body>
      <div class="container">
         <div class="slider"></div>
      </div>
   </body>
</html>
This gives the following output