SOURCE

<div class="button">
  <span>点击确定</span>
</div>

.button {
  width: 70px;
  height: 30px;
  line-height: 30px;
  border: 1px solid #0D96F2;
  position: relative;
  border-radius: 3px;
  overflow: hidden;
  text-align: center;
  cursor: pointer;
}
.button span {
  font-size: small;
  color: #0D96F2;
  transition: color 250ms 250ms linear;
}
.button:hover span {
  color: white;
}
.button::after {
  content: '';
  position: absolute;
  z-index: -1;
  width: 100%;
  height: 100%;
  bottom: 0;
  left: 0;
  background: #0D96F2;
  transform: scale(1,.1);
  transform-origin: 50% 100%;
  transition: transform 500ms ease-in-out; 
}
.button:hover::after {
  transform: scale(1,1);
}