<div class="radikalwp-f-phone"><span class="radikalwp-f-phone-prefix">+۹۸<//span><input type="tel" placeholder="۹۱۲ ۳۴۵ ۶۷۸۹"><//div>

.radikalwp-f-phone {
  display: flex;
  align-items: center;
  width: 280px;
  background: #fff;
  border: 1.5px solid #e2e8f0;
  border-radius: 12px;
  overflow: hidden;
  transition: border-color .3s ease, box-shadow .3s ease;
}
.radikalwp-f-phone:focus-within { border-color: #10b981; box-shadow: 0 0 0 4px rgba(16, 185, 129, .12); }
.radikalwp-f-phone-prefix {
  padding: 11px 14px;
  font-size: 13.5px;
  font-weight: 700;
  color: #059669;
  background: #ecfdf5;
  border-left: 1.5px solid #e2e8f0;
}
.radikalwp-f-phone input {
  flex: 1;
  min-width: 0;
  padding: 11px 14px;
  font-family: inherit;
  font-size: 13.5px;
  color: #1e293b;
  border: none;
  outline: none;
}