body {
  margin: 0;
  font-family: Arial;
  background: #0f0f0f;
  color: white;
}

nav {
  display: flex;
  justify-content: space-between;
  padding: 15px;
  background: #111;
}

button {
  margin: 5px;
  padding: 8px;
  background: #00aaff;
  border: none;
  color: white;
  cursor: pointer;
}

section {
  display: none;
  padding: 20px;
}

.active {
  display: block;
}

.card {
  background: #1c1c1c;
  padding: 12px;
  margin: 10px 0;
  border-radius: 8px;
}