<div class="radikalwp-in-group"><input type="text" placeholder="کد تخفیف" value="RWP20"><button>اعمال<//button><//div>

.radikalwp-in-group {
  display: flex;
  width: 280px;
  font-family: inherit;
  background: #fff;
  border: 1.5px solid #e2e8f0;
  border-radius: 11px;
  overflow: hidden;
  transition: border-color .3s ease, box-shadow .3s ease;
}
.radikalwp-in-group:focus-within { border-color: #f59e0b; box-shadow: 0 0 0 3px rgba(245, 158, 11, .14); }
.radikalwp-in-group input {
  flex: 1;
  min-width: 0;
  padding: 11px 14px;
  font-family: inherit;
  font-size: 13.5px;
  font-weight: 600;
  letter-spacing: 1px;
  color: #1e293b;
  border: none;
  outline: none;
}
.radikalwp-in-group input::placeholder { letter-spacing: 0; font-weight: 400; color: #94a3b8; }
.radikalwp-in-group button {
  padding: 0 22px;
  font-family: inherit;
  font-size: 13px;
  font-weight: 700;
  color: #fff;
  background: #f59e0b;
  border: none;
  cursor: pointer;
  transition: background .3s ease;
}
.radikalwp-in-group button:hover { background: #d97706; }