body {
  margin: 0;
  padding: 0;
  background: #141e30;  /* fallback for old browsers */
  background: linear-gradient(to right, #243B55, #141E30);
  height: 100vh;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

.login-box {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 350px;
  padding: 40px;
  transform: translate(-50%, -50%);
  background: rgba(0,0,0,0.75);
  box-shadow: 0 0 10px rgba(0,255,255,0.3);
  border-radius: 10px;
  color: #fff;
}

.login-box h2 {
  text-align: center;
  margin-bottom: 30px;
  font-weight: normal;
}

.user-box {
  position: relative;
  margin-bottom: 30px;
}

.user-box input {
  width: 100%;
  padding: 10px 0;
  font-size: 16px;
  color: #fff;
  background: transparent;
  border: none;
  border-bottom: 1px solid #fff;
  outline: none;
}

.user-box label {
  position: absolute;
  top: 0;
  left: 0;
  padding: 10px 0;
  font-size: 16px;
  color: #aaa;
  pointer-events: none;
  transition: 0.5s;
}

.user-box input:focus ~ label,
.user-box input:valid ~ label {
  top: -20px;
  left: 0;
  color: #03e9f4;
  font-size: 12px;
}

button {
  background: transparent;
  border: 1px solid #03e9f4;
  padding: 10px 20px;
  color: #03e9f4;
  font-size: 16px;
  cursor: pointer;
  width: 100%;
  transition: background 0.3s ease;
}

button:hover {
  background: #03e9f4;
  color: #000;
}

.error {
  color: #ff4f4f;
  text-align: center;
  margin-bottom: 15px;
}