diff --git a/src/app.css b/src/app.css
index 1738a3e43..90ad8d978 100644
--- a/src/app.css
+++ b/src/app.css
@@ -19,10 +19,23 @@ body {
   margin-inline-start: 0.53125rem;
 }
 
-#nd-toc > div > div > a > svg {
+#nd-toc > div > div > a > svg,
+#nd-toc > div > div > div.absolute {
   display: none;
 }
 
+/* Keep every active segment on one x-axis, even when labels are indented. */
+#nd-toc > div > div > a[data-active="true"]::before {
+  content: "";
+  position: absolute;
+  inset-block: -0.375rem;
+  inset-inline-start: 0.5rem;
+  width: 1px;
+  background: var(--color-fd-primary);
+  border-radius: 0;
+  z-index: 1;
+}
+
 /* Mintlify-style section labels: headings, not expandable folder controls. */
 #nd-sidebar p.inline-flex.items-center.gap-2 {
   margin-block: 1.15rem 0.35rem;
diff --git a/tests/fumapress-static-build.test.mjs b/tests/fumapress-static-build.test.mjs
index f41a4e829..19d1aa375 100644
--- a/tests/fumapress-static-build.test.mjs
+++ b/tests/fumapress-static-build.test.mjs
@@ -13,6 +13,10 @@ test("the documentation keeps a neutral base with custom section and TOC treatme
   assert.doesNotMatch(css, /fumadocs-ui\/css\/ocean\.css/);
   assert.match(css, /#nd-toc > div > div/);
   assert.match(css, /#nd-toc > div > div > a > svg/);
+  assert.match(css, /#nd-toc > div > div > div\.absolute/);
+  assert.match(css, /a\[data-active="true"\]::before/);
+  assert.match(css, /inset-inline-start: 0\.5rem/);
+  assert.match(css, /border-radius: 0/);
 });
 
 async function collectHtmlRoutes(directory) {