/* Top-level headers remain the same dark blue */
.top-header {
  background-color: #003366; /* your current dark blue */
  color: white;
  height: 40px; /* example height */
}

/* Nested headers get lighter dark blue and smaller height */
.nested-header {
  background-color: #335588; /* lighter version */
  color: white;
  height: 28px; /* smaller height */
}