* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: Arial, sans-serif;
  background: #f4f4f9;
  color: #333;
}

header {
  background: #333;
  color: #fff;
  padding: 15px 0;
  text-align: center;
}

nav ul {
  list-style: none;
  display: flex;
  justify-content: center;
  margin-top: 10px;
}

nav ul li {
  margin: 0 15px;
}

nav ul li a {
  color: #fff;
  text-decoration: none;
  font-weight: bold;
  padding: 6px 10px;
  border-radius: 3px;
  transition: background 0.3s;
}

nav ul li a:hover {
  background: #555;
}

main {
  max-width: 900px;
  margin: 20px auto;
  padding: 20px;
  background: #fff;
  border-radius: 5px;
  box-shadow: 0 0 5px rgba(0,0,0,0.1);
}

section {
  display: none; /* hidden until selected */
}

h2 {
  margin-bottom: 10px;
  color: #444;
}

ul {
  margin-top: 10px;
  padding-left: 20px;
}

footer {
  text-align: center;
  padding: 15px;
  margin-top: 20px;
  background: #333;
  color: #fff;
}