/* Element selector */
body {
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
  background: #f7f9fc;
  color: #1f2937;
  margin: 24px;
  line-height: 1.6;
}

/* ID selector */
#page-header {
  background: #111827;
  color: #ffffff;
  padding: 16px 20px;
  border-radius: 10px;
}

/* Class selectors */
.card {
  background: #ffffff;
  border: 1px solid rgba(0,0,0,0.06);
  border-radius: 10px;
  padding: 16px 20px;
  margin: 16px 0;
  box-shadow: 0 6px 14px rgba(0,0,0,0.06);
}

.subtitle {
  margin: 6px 0 0;
  font-style: italic;
  color: #d1d5db;
}

.rules {
  padding-left: 1.25rem;
  list-style: square;
}

.diagram {
  display: block;
  max-width: 100%;
  height: auto;
  margin: 12px 0;
}

footer {
  margin-top: 24px;
  font-size: 0.95rem;
  color: #4b5563;
}