library_books<style>
  @keyframes translateY{
    0%,100%{transform:translateY(0px)}
    50%{transform:translateY(150px)}
  }
  div {
    width:40px;height:40px;
    border-radius:50%;
    background:#639;
    margin:auto;
    animation:translateY 2s linear infinite;
  }
 </style>
 <div></div>

library_books<style>
  @keyframes translateY{
    0%,100%{transform:translateY(0px)}
    50%{transform:translateY(150px)}
  }
  div {
    width:35px;height:35px;
    border: 5px solid #00ffc9;
    border-radius:50%;
    background:#639;
    margin:auto;
    animation:translateY 2s linear infinite;
  }
 </style>
 <div></div>