<form class="radikalwp-f-news"><input type="email" placeholder="ایمیل شما"><button>عضویت<//button><//form>

.radikalwp-f-news {
  display: flex;
  width: 300px;
  background: #fff;
  border: 1.5px solid #e2e8f0;
  border-radius: 12px;
  padding: 5px;
  transition: border-color .3s ease, box-shadow .3s ease;
}
.radikalwp-f-news:focus-within { border-color: #0ea5e9; box-shadow: 0 0 0 4px rgba(14, 165, 233, .12); }
.radikalwp-f-news input {
  flex: 1;
  min-width: 0;
  padding: 8px 12px;
  font-family: inherit;
  font-size: 13px;
  color: #1e293b;
  border: none;
  outline: none;
  background: transparent;
}
.radikalwp-f-news button {
  padding: 9px 20px;
  font-family: inherit;
  font-size: 13px;
  font-weight: 700;
  color: #fff;
  background: #0ea5e9;
  border: none;
  border-radius: 9px;
  cursor: pointer;
  transition: background .3s ease;
}
.radikalwp-f-news button:hover { background: #0284c7; }