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HTML

              
                <ul>
  <li>first...</li>
  <li>second...</li>
  <li>third...</li>
</ul>
              
            
!

CSS

              
                @keyframes show {
    0% {opacity: 0;}
    20% {opacity: 1;}
    80% {opacity: 1;}
    100% {opacity: 0;}
}

li {
  display: none;
}

li.animate {
    animation: show 3s linear;
    display: inline-block;
}
              
            
!

JS

              
                var slideIndex = 0;
// Here you select all the HTML elements you want to use as slides
// querySelectorAll is a good choice 
//as it allows you to select elements using CSS selectors, I kinda love it!
var all = document.querySelectorAll("li");

// Ok, let's start calling the function, so that it starts right away
carousel();

// This function simply adds a CSS class and removes it as the timeout ends, 
// be careful, it should be the same as the CSS animation you're going to build, 
// or else it won't allow to show the full animation.
function carousel() {
  var i;
  // Let's remove the class to each element first
  for (i = 0; i < all.length; i++) {
    all[i].classList.remove("animate");
  }
  // Then increment the slide idex (which element you want to animate)
  slideIndex++;
  // Of course you have to go to the first element if you reach the end.
  if (slideIndex > all.length) {slideIndex = 1}
  // Add the class to the current index element.
  all[slideIndex-1].classList.add("animate");
  setTimeout(carousel, 3000);
}
              
            
!
999px

Console