body {
  line-height: 1.45;
  font-family: Ubuntu, sans-serif;
  font-size: 17px;
  color: #252525;
}

.block {
  padding: 16px; 
  animation-name: jump;
  animation-duration: 1.75s;
  animation-timing-function: linear;
  animation-delay: 2.5s;
  animation-direction: alternate;
  animation-fill-mode: both; 
}

.block..block-1 {
  animation-iteration-count: 2;
}

.block.block-2 {
  animation-iteration-count: 15;
}

@keyframes jump {
  from {
    margin-top: 0;
    background-color: #666;
    color: #f1f1f1;
  }
  to {
    margin-top: 15%;
    background-color: #808080;
    color: #252525;
  }
}