body {
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
}

header {
  background-color: #333;
  color: #fff;
  padding: 1rem;
}

nav a:link,
nav a:visited {
  color: white;
  text-decoration: none;
}

nav a:hover,
nav a:active {
  color: #dddddd;
  text-decoration: none;
}

main {
  padding: 1rem;
}

h1, h2 {
  margin-top: 0;
}

.error-message {
  color: red;
  font-size: 14px;
  display: block;
  margin-top: 5px;
}

#result {
  color: #00aa00;
  font-weight: bold;
  font-size: 24px;
  margin-top: 10px;
}