CSS Animatable opacity Property Example

<!DOCTYPE html>
<html>
<head>
<style>
#grid-container {
	display: grid;
    grid-template-columns: auto auto auto;
    background: #333;
    grid-gap: 20px;
    padding: 20px;
    margin: 20px;
    box-shadow: 0 0 10px 0 #aaa;
    border-radius: 20px;
}
  
#grid-container div {
    width: 50px;
    height: 50px;
    text-align: center;
    line-height: 50px;
    font-size: 20px;
    background: red;
    border-radius: 50px;
    margin: auto;
}

#item1 {animation: anim 5s infinite;}
#item2 {animation: anim 5s infinite; animation-delay: 0.3s;}
#item3 {animation: anim 5s infinite; animation-delay: 0.6s;}
#item4 {animation: anim 5s infinite; animation-delay: 0.9s;}
#item5 {animation: anim 5s infinite; animation-delay: 1.2s;}
#item6 {animation: anim 5s infinite; animation-delay: 1.5s;}
#item7 {animation: anim 5s infinite; animation-delay: 1.8s;}
#item8 {animation: anim 5s infinite; animation-delay: 2.1s;}
#item9 {animation: anim 5s infinite; animation-delay: 2.4s;}

@keyframes anim {
    50% {opacity: 0;}
}
</style>
</head>
<body>

<h1>Animatable 'opacity' Property</h1>
<hr>

<p>Experience the changing opacity of the grid items.</p>
  
<div id="grid-container">
  	<div id="item1">1</div>
  	<div id="item2">2</div>
  	<div id="item3">3</div>
  	<div id="item4">4</div>
  	<div id="item5">5</div>
  	<div id="item6">6</div>
  	<div id="item7">7</div>
  	<div id="item8">8</div>
  	<div id="item9">9</div>
</div>

</body>
</html>