button {
  position: relative;
  overflow: hidden;
  border: none;
  color: #3b5998;
  display: inline-block;
  font-size: 15px;
  line-height: 15px;
  padding: 18px 18px 17px;
  text-decoration: none;
  cursor: pointer;
  background: #fff;
  user-select: none;
  -webkit-user-select: none;
  touch-action: manipulation;
}

button span:first-child {
  position: relative;
  transition: color 600ms cubic-bezier(0.48, 0, 0.12, 1);
  z-index: 10;
}
button:hover {
  color: #fff;
}

button:after {
  content: "";
  position: absolute;
  bottom: -50%;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: #3b5998;
  transform-origin: bottom center;
  transition: transform 600ms cubic-bezier(0.48, 0, 0.12, 1);
  transform: skewY(9.3deg) scaleY(0);
  z-index: 1;
}

button:hover:after {
  transform-origin: bottom center;
  transform: skewY(9.3deg) scaleY(2);
}