book.css

/* Quarto auto-numbers each book chapter, so the page title renders as
     <span class="chapter-number">1</span>&nbsp; <span class="chapter-title">…</span>
   The bare "1" is redundant with our Part/Module grouping, so we hide it — but
   hiding the number span alone leaves the "&nbsp; " text node that followed it
   as leading whitespace before the title. We collapse that whitespace by
   zeroing the h1's font size and restoring the visible title span.

   Scope notes:
   - .chapter-number is hidden globally (page title AND sidebar).
   - The font-size:0 collapse is scoped with :has(.chapter-number) so it only
     touches chapter titles — the landing page's <h1 class="title"> holds raw
     text (no .chapter-title span) and must not be zeroed.
   - The restore is scoped to `h1.title .chapter-title`, so sidebar chapter
     links (which use .chapter-title outside any h1.title) are untouched.
   - Section numbers (.header-section-number, e.g. 1.2.8) are left intact. */
.chapter-number {
  display: none;
}

h1.title:has(.chapter-number) {
  font-size: 0; /* collapses the dangling "&nbsp; " left by the hidden number */
}

/* Restore Bootstrap/cosmo's responsive h1 size on the visible title text. */
h1.title .chapter-title {
  font-size: calc(1.325rem + 0.9vw);
}
@media (min-width: 1200px) {
  h1.title .chapter-title {
    font-size: 2rem;
  }
}