.arrow {
    height: 20px;
    width: 20px; 
    border: 2px solid black;
    background-color: red;
    border-radius: 50%;
    display: inline-block;
    animation:arrowAnimation 2s infinite;  
    transition: transform 330ms ease-in-out;
  }
  
@keyframes arrowAnimation{
    0%{     transform: scale(1); background-color: rgb(255, 0, 0);  }
    50%{    transform: scale(1.5); background-color: rgb(109, 2, 20); }
    100%{   transform: scale(1); background-color:red;  }
}