#particles-js {
  position: absolute;
  width: 30%;
  height: 100%;
  z-index: 900;
  left: 0;
}
#particles-js2 {
  position: absolute;
  width: 30%;
  height: 100%;
  z-index: 900;
  right: 0;
}

@media all and (max-width: 800px) {
    #particles-js,#particles-js2{z-index: 800}
}