SOURCE

body{
  height: 100vh;
  margin: 0px;
  padding: 0px;
  background: radial-gradient(#eee,#444);
}
body:before{
  content: '';
  opacity: 0.5;
  display: block;
  width: 50vw;
  height: 100px;
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%,-50%);
  background-image: repeating-linear-gradient(90deg, transparent 0 20px, black 20px 40px);
  animation: waves 3s infinite;
}

 @keyframes waves {
  from { opacity: 0.5; transform: translate(-50%,-50%) scaleY(0.1); }
  50% { opacity: 0.1; transform: translate(-50%,-50%) scaleY(1); }
  to { opacity: 0.5; transform: translate(-50%,-50%) scaleY(0.1); }
}