<form class="radikalwp-f-login"><h4>خوش آمدید<//h4><div class="radikalwp-f-login-field"><input type="text" placeholder="نام کاربری"><i><//i><//div><div class="radikalwp-f-login-field"><input type="password" placeholder="رمز عبور"><i><//i><//div><button>ورود به حساب<//button><//form>

.radikalwp-f-login {
  width: 280px;
  padding: 24px;
  font-family: inherit;
  background: #fff;
  border: 1px solid #e2e8f0;
  border-radius: 14px;
}
.radikalwp-f-login h4 { margin: 0 0 18px; font-size: 17px; color: #1e293b; text-align: center; }
.radikalwp-f-login-field { position: relative; margin-bottom: 18px; }
.radikalwp-f-login-field input {
  width: 100%;
  padding: 10px 2px;
  font-family: inherit;
  font-size: 13.5px;
  color: #1e293b;
  background: transparent;
  border: none;
  border-bottom: 2px solid #e2e8f0;
  outline: none;
  transition: border-color .3s ease;
}
.radikalwp-f-login-field input:focus { border-bottom-color: #6366f1; }
.radikalwp-f-login-field i {
  position: absolute;
  bottom: -2px;
  right: 0;
  width: 0;
  height: 2px;
  background: #6366f1;
  transition: width .35s ease;
}
.radikalwp-f-login-field input:focus ~ i { width: 100%; }
.radikalwp-f-login button {
  width: 100%;
  padding: 11px;
  font-family: inherit;
  font-size: 14px;
  font-weight: 700;
  color: #fff;
  background: #6366f1;
  border: none;
  border-radius: 10px;
  cursor: pointer;
  transition: background .3s ease;
}
.radikalwp-f-login button:hover { background: #4f46e5; }