.button {
  padding: 12px 25px;
  background: #fff;
  border: 1px solid #121212;
  color: #121212;
  font-weight: 700;
  cursor: pointer;
  border-radius: 50px;
  position: relative;
  z-index: 2;
  overflow: hidden;
  transition: all 0.5s ease;
}
.button::after {
  content: "";
  width: 100%;
  height: 100%;
  background: #121212;
  position: absolute;
  bottom: -100%;
  left: 0;
  border-radius: 50%;
  z-index: -1;
  transition: all 0.5s ease;
}
.button:hover {
  color: #fff;
}
.button:hover::after {
  bottom: 0;
  border-radius: 0;
}