@keyframes animate {
  
  from { 
    margin-top: 50px; 
  }
  
  50%  {
    /* ignored */
    margin-top: 150px !important; 
  }
  
  to   { 
    margin-top: 100px; 
  }
  
}

.block {
  background-color: red;
  padding: 36px 26px;
  width: 75px;
  text-align: center;
  color: #fff;
  font-size: 18px;
  border: 2px solid rgba(255, 255, 255, .45);
  animation: animate 1s ease-in 0s infinite alternate;
}