<div class="radikalwp-input-group"><input type="email" class="radikalwp-input-group-field" placeholder="ایمیل شما"><button class="radikalwp-input-group-btn" type="button">عضویت<//button><//div>

.radikalwp-input-group {
  display: flex; width: 320px; max-width: 100%; background: #fff; border: 1.5px solid #cbd5e1;
  border-radius: 14px; overflow: hidden; transition: border-color .2s;
}
.radikalwp-input-group:focus-within { border-color: #4f46e5; }
.radikalwp-input-group-field {
  flex: 1; padding: 12px 16px; font-size: 13px; font-family: inherit; color: #1e293b;
  border: 0; outline: none; min-width: 0;
}
.radikalwp-input-group-btn {
  padding: 0 22px; background: #4f46e5; color: #fff; font-size: 13px; font-weight: 700;
  border: 0; cursor: pointer; font-family: inherit; transition: background .2s;
}
.radikalwp-input-group-btn:hover { background: #4338ca; }