body {
  font-family: system-ui, sans-serif;
  background: #f4f7fb;
  margin: 0;
  color: #222;
}
header {
  background: #4a6fa5;
  color: white;
  padding: 1em;
  text-align: center;
}
nav {
  display: flex;
  justify-content: center;
  gap: 1em;
  background: #e0e6ef;
  padding: 0.5em;
}
button {
  padding: 0.6em 1em;
  border: none;
  border-radius: 6px;
  background: #4a6fa5;
  color: white;
  cursor: pointer;
}
button:hover { background: #395a86; }
main { padding: 1em; max-width: 900px; margin: auto; }
.module { display: none; }
.module.active { display: block; }
.card {
  background: white;
  padding: 1em;
  border-radius: 8px;
  margin-bottom: 1em;
}