/* Hide all sections by default */
#main-content section {
  display: none;
}

/* Show active section */
#main-content section.active {
  display: block;
  animation: fadeIn 0.3s ease-out;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: translateY(0); }
}