.orangeballoon {
  background-image: url(orange_balloon.png);
  width: 180px;
  height: 180px;
  // border-style: solid;
  // border-color: red;
  text-align: center;
  line-height: 180px;
  background-size: contain;
  position: absolute;
  z-index:-1;
  bottom: 0%;
  animation: move_y 30s linear forwards, oscil1 9s infinite;
  left: 45%;
}
.blueballoon {
  background-image: url(blue_balloon.png);
  width: 140px;
  height: 140px;
  text-align: center;
  line-height: 140px;
  background-size: contain;
  position: absolute;
  bottom: 0%;
  animation: move_y 10s linear forwards, oscil1 9s infinite;
  left: 25%;
}

.greenballoon {
  background-image: url(green_balloon.png);
  width: 120px;
  height: 120px;
  text-align: center;
  line-height: 120px;
  background-size: contain;
  position: absolute;
  bottom: 25%;
  animation: move_y 15s linear forwards, oscil1 9s infinite;
  left: 65%;
}

@keyframes move_y {
  from {
    bottom: -10%;
  }
  to {
    bottom: 100%;
  }
}

@keyframes oscil1 {
  from {
    translate: 0 0;
    transform: rotate(0deg);
    animation-timing-function: cubic-bezier(0.1, 0.3, 0.3, 1);
  }
  25% {
    translate: 10px 0;
    transform: rotate(3deg);
    animation-timing-function: cubic-bezier(0.7, 0.0, 0.9, 0.7);
  }
  50% {
    translate: 0 0;
    transform: rotate(0deg);
    animation-timing-function: cubic-bezier(0.1, 0.3, 0.3, 1);
  }
  75% {
    translate: -10px 0;
    transform: rotate(-3deg);
    animation-timing-function: cubic-bezier(0.7, 0.0, 0.9, 0.7);
  }
  to {
    translate: 0 0;
    transform: rotate(0deg);
  }
}