body {
  font-family: Arial, sans-serif;
  background-color: #f4f4f4;
  margin: 0;
  padding: 0;
}

header {
  background-color: #4CAF50;
  color: white;
  padding: 20px;
  text-align: center;
}

nav {
  margin-top: 10px;
}

nav a {
  margin: 0 10px;
  color: white;
  text-decoration: none;
  font-weight: bold;
}

nav a:hover {
  text-decoration: underline;
}

main {
  padding: 20px;
  background-color: white;
  max-width: 900px;
  margin: auto;
  box-shadow: 0 0 10px rgba(0,0,0,0.1);
}

.ad-banner {
  background: #fff3cd;
  border: 2px dashed #ffeeba;
  text-align: center;
  padding: 10px;
  margin: 20px 0;
}

footer {
  background-color: #eee;
  text-align: center;
  padding: 15px;
  font-size: 14px;
  margin-top: 40px;
}