* {
  box-sizing: border-box;
}

body {
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  background: linear-gradient(135deg, #667eea, #764ba2);
  margin: 0;
  padding: 0;
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
}

.container {
  background: #ffffff;
  padding: 40px 30px;
  border-radius: 12px;
  box-shadow: 0 10px 25px rgba(0, 0, 0, 0.2);
  width: 320px;
  animation: fadeIn 0.8s ease;
}

@keyframes fadeIn {
  from { opacity: 0; transform: scale(0.75); }
  to { opacity: 1; transform: scale(1); }
}

h2 {
  margin: 0 0 20px;
  text-align: center;
  color: #333;
}

input {
  width: 100%;
  padding: 12px;
  margin: 10px 0;
  border: 1px solid #ccc;
  border-radius: 8px;
  font-size: 15px;
  transition: border-color 0.3s;
}

input:focus {
  border-color: #667eea;
  outline: none;
}

button {
  width: 100%;
  padding: 12px;
  background-color: #667eea;
  border: none;
  color: white;
  font-weight: bold;
  border-radius: 8px;
  font-size: 16px;
  margin-top: 15px;
  cursor: pointer;
  transition: background-color 0.3s;
}

button:hover {
  background-color: #5a67d8;
}

#error, #thongbao {
  margin-top: 10px;
  text-align: center;
  color: crimson;
  font-weight: bold;
}