body {
  font-family: 'JetBrains Mono', Optima, Segoe UI, Candara, Calibri, sans-serif;
  margin: 0;
  padding: 0;
  background: #f5f5f5;
  color: #222;
  transition: background 0.3s, color 0.3s;
}
header {
  background: #333;
  color: white;
  padding: 1rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
button#toggle-dark {
  background: #555;
  color: white;
  border: none;
  padding: 0.5rem 1rem;
  cursor: pointer;
}
.grid {
  display: flex;
  flex-wrap: wrap;
  gap: 2rem;
  padding: 2rem;
}
.os {
  flex: 1 1 30%;
  background: white;
  border: 1px solid #ccc;
  padding: 1rem;
  border-radius: 8px;
}
.level {
  margin-top: 1rem;
}
.level h3 {
  margin-bottom: 0.5rem;
}
body.dark-mode {
  background: #121212;
  color: #eee;
}
body.dark-mode .os {
  background: #1e1e1e;
  border-color: #444;
}
body.dark-mode header {
  background: #222;
}
body.dark-mode button#toggle-dark {
  background: #888;
}