How to create Animated Background using CSS and HTML

In this Blog, we are going to learn how to create Animated Background using CSS and HTML.
First of all, create an HTML File and paste the below code.
HTML CODE:

<!DOCTYPE html>
<html lang='en'>
<head>
<meta charset='UTF-8'>
<meta name="robots" content="noindex">

</head>

<body>
<div class="context">
<h1>Animated Background Using CSS</h1>
</div>

<div class="area" >
<ul class="circles">
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
</ul>
</div >
</body>
</html>

Now create a CSS file and paste the below code.

@import url('https://fonts.googleapis.com/css?family=Exo:400,700');

*{
margin: 0px;
padding: 0px;
}

body{
font-family: 'Exo', sans-serif;
}


.context {
width: 100%;
position: absolute;
top:50vh;

}
.context h1{
text-align: center;
color: #fff;
font-size: 50px;
}
.area{
background: #4e54c8; 
background: -webkit-linear-gradient(to left, #8f94fb, #4e54c8); 
width: 100%;
height:100vh;
}

.circles{
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
overflow: hidden;
}

.circles li{
position: absolute;
display: block;
list-style: none;
width: 20px;
height: 20px;
background: rgba(255, 255, 255, 0.2);
animation: animate 25s linear infinite;
bottom: -150px;
}

.circles li:nth-child(1){
left: 25%;
width: 80px;
height: 80px;
animation-delay: 0s;
}


.circles li:nth-child(2){
left: 10%;
width: 20px;
height: 20px;
animation-delay: 2s;
animation-duration: 12s;
}

.circles li:nth-child(3){
left: 70%;
width: 20px;
height: 20px;
animation-delay: 4s;
}

.circles li:nth-child(4){
left: 40%;
width: 60px;
height: 60px;
animation-delay: 0s;
animation-duration: 18s;
}

.circles li:nth-child(5){
left: 65%;
width: 20px;
height: 20px;
animation-delay: 0s;
}

.circles li:nth-child(6){
left: 75%;
width: 110px;
height: 110px;
animation-delay: 3s;
}

.circles li:nth-child(7){
left: 35%;
width: 150px;
height: 150px;
animation-delay: 7s;
}

.circles li:nth-child(8){
left: 50%;
width: 25px;
height: 25px;
animation-delay: 15s;
animation-duration: 45s;
}

.circles li:nth-child(9){
left: 20%;
width: 15px;
height: 15px;
animation-delay: 2s;
animation-duration: 35s;
}

.circles li:nth-child(10){
left: 85%;
width: 150px;
height: 150px;
animation-delay: 0s;
animation-duration: 11s;
}

@keyframes animate {

0%{
transform: translateY(0) rotate(0deg);
opacity: 1;
border-radius: 0;
}

100%{
transform: translateY(-1000px) rotate(720deg);
opacity: 0;
border-radius: 50%;
}

}

Output: