<button class="bhe-01__btn">Hover Me</button>

.bhe-01__btn {
  padding: 12px 32px;
  font-size: 13.5px;
  font-family: inherit;
  font-weight: 500;
  border-radius: 8px;
  cursor: pointer;
  letter-spacing: 0.02em;
  background: transparent;
  color: inherit;
}

.bhe-01__btn {
  position: relative;
  color: #7c6cff;
  background: transparent;
  border: 2px solid #7c6cff;
  overflow: hidden;
  transition: color 0.4s;
  z-index: 0;
}
.bhe-01__btn::before {
  content: "";
  position: absolute;
  bottom: -2px;
  left: -2px;
  right: -2px;
  height: 0;
  background: #7c6cff;
  transition: height 0.45s cubic-bezier(0.23, 1, 0.32, 1);
  z-index: -1;
}
.bhe-01__btn:hover {
  color: #fff;
}
.bhe-01__btn:hover::before {
  height: calc(100% + 4px);
}