.balls {
    border-radius: 50%;
    position: fixed;
    width: 50px;
    height: 50px;
    top: 60%;
    animation-name: jump;
    animation-duration: 2s;
    animation-iteration-count: infinite;
  }

  #red {
    background: red;
    left: 25%;
    animation-timing-function: linear;
  }

  #blue {
    background: blue;
    left: 50%;
    animation-timing-function: ease-out;
  }

  #green {
    background: green;
    left: 75%;
    animation-timing-function: cubic-bezier(0.311, 0.441, 0.444, 1.649);
  }

  @keyframes jump {
    50% {
      top: 10%;
    }
  }

  #black {
    position: absolute;
    z-index: -10;
    padding: 0;
    margin: 0;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(black, #000099, #66c2ff, #ffcccc, #ffeee6);
}