SOURCE

<div class="hero">
  <div class="parallax-layer layer-6"></div>
</div>

* {
  box-sizing: border-box;
}
body {
  font-family: 'Lato', sans-serif;
}
.hero {
  width: 100%;
  height:100%;
  min-height: 450px;
  position: relative;
  top: 0;
  left: 0;
  background-color: #d9edfd;
  transform: translate3d(0,0,0); 
}

  .layer-6 {
    animation: parallax_fg linear 10s infinite both;
    background:  url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/24650/6.png) 0 100% repeat-x;
    z-index: 1;
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-size:  auto 222px;
  }

@keyframes parallax_fg {  
  0% { background-position: 2765px 100%;} 
  100% {background-position: 550px 100%; } 
}