/* ── Open textbooks (templates/books/textbooks.html, textbook.html) ──
   The library's own look (books.css); here only what the textbooks add:
   the filters beside the search box, and a book's contents by depth. */
.tb-filters { flex-wrap: wrap; align-items: center; }
.tb-filters select {
  font: inherit;
  font-size: var(--step--1);
  padding: 0.55rem 0.6rem;
  border-radius: var(--radius);
  border: 1px solid var(--border-strong);
  background: var(--surface);
  color: var(--text);
  max-width: 100%;
}
.tb-contents { padding: 0 var(--gutter) 0 calc(var(--gutter) + 1.5rem); margin: 0; line-height: 1.5; max-width: 60rem; }
.tb-contents li { padding: 0.15rem 0; }
.tb-contents a { color: var(--accent-text); text-decoration: underline; text-underline-offset: 0.15em; }
.tb-contents .tb-depth-0 { font-weight: 600; margin-top: 0.5rem; }
.tb-contents .tb-depth-1 { margin-left: 1rem; }
.tb-contents .tb-depth-2, .tb-contents .tb-depth-3 { margin-left: 2rem; font-size: var(--step--1); }