body {
  font-family: Arial, sans-serif;
  background: #f4f4f4;
  margin: 0;
  padding: 0;
}
.container {
  max-width: 400px;
  margin: 40px auto;
  background: #fff;
  padding: 2em;
  border-radius: 8px;
  box-shadow: 0 2px 8px #0001;
}
h1 {
  text-align: center;
}
form {
  display: flex;
  flex-direction: column;
  gap: 1em;
}
input[type="text"] {
  padding: 0.5em;
  font-size: 1em;
  border: 1px solid #ccc;
  border-radius: 4px;
}
button {
  padding: 0.7em;
  font-size: 1em;
  background: #2d8cf0;
  color: #fff;
  border: none;
  border-radius: 4px;
  cursor: pointer;
}
button:hover {
  background: #1a6fb3;
}
.qr-preview {
  text-align: center;
  margin: 1.5em 0;
}
.error {
  color: #d00;
  text-align: center;
}