<button class="radikalwp-btn-fold">دانلود رایگان<//button>

.radikalwp-btn-fold {
  position: relative;
  padding: 12px 30px;
  font-family: inherit;
  font-size: 15px;
  font-weight: 700;
  color: #fff;
  background: #0ea5e9;
  border: none;
  border-radius: 12px;
  cursor: pointer;
  transition: background .25s ease, transform .2s ease;
}
.radikalwp-btn-fold::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  border-style: solid;
  border-width: 0 18px 18px 0;
  border-color: transparent #0369a1 transparent transparent;
  border-radius: 0 0 12px 0;
}
.radikalwp-btn-fold:hover {
  background: #0284c7;
  transform: translateY(-1px);
}