<html lang="en">
<head>
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <meta http-equiv="X-UA-Compatible" content="ie=edge">
   <title>Rain background</title>
   <link rel="stylesheet" href="./style.css">
</head>
<body>
<section>
</section>
</body>
</html>
*{
   margin: 0px;
   padding: 0px;
   box-sizing: border-box;
}

section{
   position: relative;
   height: 100vh;
   width: 100%;
   background-image: url('https://www.thisiscolossal.com/wp-content/uploads/2018/11/HenriPrestes_02.jpg');
   background-repeat: no-repeat;
   background-size: cover;
   background-position: center;
}

section::before{
   content: '';
   position: absolute;
   top: 0%;
   left: 0%;
   width: 100%;
   height: 100%;
   background-image: url('http://pngimg.com/uploads/rain/rain_PNG13468.png');
   animation: rain 0.19s ease-in infinite;
}

@keyframes rain{
   0%{
      background-position: 10 0;
   }
   100%{
      background-position: 20% 80%;
   }
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.