<div>
  <button onClick="this.focus()">CLICK<span>FADE IN</span></button>
  <button onClick="this.focus()">CLICK<span>FADE IN</span></button>
  <button onClick="this.focus()">CLICK<span>FADE IN</span></button>
</div>
body {
  overflow:hidden;
}

div {
  position:absolute;
  top:50%;
  left:50%;
  transform: translate(-50%,-50%);
  white-space: nowrap;
}
button {
  position: relative;
  margin: 0 3vw;
  width:16vw;
  height:8vw;
  line-height: 8vw;
  background: #333;
  border-radius: 1vw;
  text-align: center;
  color: #fff;
  font-size:2.5vw;
  font-weight: bold;
  border: 0;
}
button span {
  position:absolute;
  display: block;
  color: #333;
  text-align: center;
  top:50%;
  left:50%;
  transform: translate(-50%,-50%);
  width: 22vw;
  height:11vw;
  line-height: 11vw;
  background: #ccc;
  border-radius: 2vw;
  border: 2px solid #333;
  box-sizing: border-box;
  opacity:0;
}
button:focus {
  outline: none;
}
button:focus span {
  animation: fadeIn .5s forwards;
}

@keyframes fadeIn {
  0% {
    margin-top:50px;
    opacity: 0;
  }
  100% {
    margin-top:0;
    opacity: 1;
  }
}

External CSS

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External JavaScript

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