*{
  margin: 0;
  padding: 0;
}
section.wave {
  position: relative;
  width: 100%;
  height: 11vh;
  background: var(--dark-bg);
  overflow: hidden;
}
section.wave .air{
  position: absolute;
  bottom: 0;
  left: 0;
  width: 100%;
  height: 100px;
  background: url(https://1.bp.blogspot.com/-xQUc-TovqDk/XdxogmMqIRI/AAAAAAAACvI/AizpnE509UMGBcTiLJ58BC6iViPYGYQfQCLcBGAsYHQ/s1600/wave.png);
  background-size: 1000px 100px
}
section.wave .air.air1{
  animation: wave 30s linear infinite;
  z-index: 1000;
  opacity: 1;
  animation-delay: 0s;
  bottom: 0;
}
section.wave .air.air2{
  animation: wave2 15s linear infinite;
  z-index: 999;
  opacity: 0.5;
  animation-delay: -5s;
  bottom: 10px;
}
section.wave .air.air3{
  animation: wave 30s linear infinite;
  z-index: 998;
  opacity: 0.2;
  animation-delay: -2s;
  bottom: 15px;
}
section.wave .air.air4{
  animation: wave2 5s linear infinite;
  z-index: 997;
  opacity: 0.7;
  animation-delay: -5s;
  bottom: 20px;
}
@keyframes wave {
  0%{
    background-position-x: 0px; 
  }
  100%{
    background-position-x: 1000px; 
  }
}
@keyframes wave2 {
  0%{
    background-position-x: 0px; 
  }
  100%{
    background-position-x: -1000px; 
  }
}

section.wave {
    position: absolute;
    z-index: -999;
    bottom:0;
}