Reduce navigation size

public/docs/css/main.css

@@ -1300,6 +1300,19 @@ li.has-children .sub-nav ul li:focus > a {
   padding-block: var(--gap-menu);
 }
 
+/* Right-chevron on top-level section links (navigate, not expand). */
+.site-nav
+  > .site-nav__list
+  > .site-nav__list-item:not(.has-children)
+  > a::after {
+  content: '\f054';
+  /* Chevron Right */
+  font-family: fa-solid;
+  float: right;
+  color: var(--color-menu-marker);
+  margin-inline-end: 0.5rem;
+}
+
 .site-nav details[open] > summary {
   background-color: var(--bg-color-menu-open);
   font-weight: bold;

src/themes/octopus/components/Navigation.astro

@@ -1,5 +1,6 @@
 ---
 import { Accelerator } from 'astro-accelerator-utils';
+import type { NavPage } from 'astro-accelerator-utils/types/NavPage';
 import { Translations, Lang } from '@util/Languages';
 import { menu } from '@data/navigation';
 import NavigationItem from '@components/NavigationItem.astro';
@@ -9,19 +10,45 @@ const accelerator = new Accelerator(SITE);
 const stats = new accelerator.statistics('octopus/components/Navigation.astro');
 stats.start();
 
-// Properties
 type Props = {
   lang: string;
 };
 const { lang } = Astro.props satisfies Props;
 
-// Language
 const _ = Lang(lang);
 
-// Logic
 const currentUrl = new URL(Astro.request.url);
 const pages = accelerator.navigation.menu(currentUrl, SITE.subfolder, menu);
 
+// Expand the current section in place; collapse every other section to a
+// labelled link.
+const currentPath = currentUrl.pathname.replace(/\/$/, '');
+function isOnActivePath(page: NavPage): boolean {
+  const pUrl = (page.url ?? '').replace(/\/$/, '');
+  if (!pUrl) return false;
+  return currentPath === pUrl || currentPath.startsWith(pUrl + '/');
+}
+function markActiveBranchOpen(items: NavPage[]): void {
+  for (const item of items) {
+    if (item.children && item.children.length > 0 && isOnActivePath(item)) {
+      item.isOpen = true;
+      markActiveBranchOpen(item.children);
+    }
+  }
+}
+
+for (const top of pages) {
+  if (top.children && top.children.length > 0) {
+    if (isOnActivePath(top)) {
+      top.isOpen = true;
+      markActiveBranchOpen(top.children);
+    } else {
+      if (top.section) top.title = top.section;
+      top.children = [];
+    }
+  }
+}
+
 stats.stop();
 ---