body {
  font-family: Arial, sans-serif;
  margin: 0;
  background: #f4f6f8;
}
header {
  background: #0b3c5d;
  color: white;
  padding: 20px;
  text-align: center;
}
nav {
  background: #062f4f;
  padding: 10px;
  text-align: center;
}
nav button {
  margin: 0 5px;
  padding: 8px 15px;
  border: none;
  background: #ffffff;
  cursor: pointer;
  font-weight: bold;
}
main {
  padding: 20px;
  max-width: 900px;
  margin: auto;
}
article {
  background: white;
  padding: 15px;
  margin-bottom: 15px;
  border-radius: 6px;
}
footer {
  background: #062f4f;
  color: white;
  text-align: center;
  padding: 10px;
}
.hidden {
  display: none;
}