<button class="radikalwp-btn-outlinefill">دانلود کاتالوگ<//button>

.radikalwp-btn-outlinefill {
  padding: 12px 34px;
  font-family: inherit;
  font-size: 15px;
  font-weight: 700;
  color: #7c3aed;
  background: linear-gradient(to left, #7c3aed 50%, transparent 50%);
  background-size: 200% 100%;
  background-position: left;
  border: 2px solid #7c3aed;
  border-radius: 12px;
  cursor: pointer;
  transition: background-position .35s ease, color .35s ease;
}
.radikalwp-btn-outlinefill:hover {
  background-position: right;
  color: #fff;
}