i don't rember

static/css/tree.css

@@ -1,17 +1,11 @@
-/* The tree indents shouldn't be too spaced out */
-
 .tree ul {
     padding-left: clamp(12px, 2vw, 24px);
 }
 
-/* But the first block should not be indented. */
-
 .tree>ul {
     padding-left: 0;
 }
 
-/* Make the tree have + and - instead of the default details/summary arrow */
-
 .tree {
     --tree-icon-position: 8px 50%;
     --tree-icon-space: 28px;
@@ -76,7 +70,7 @@
     background-color: rgba(0, 0, 0, 5%);
 }
 
-.tree li.leaf {
+.tree li>div {
     background-image: url('../svg/leaf.svg');
     background-repeat: no-repeat;
     background-position: var(--tree-icon-position);
@@ -157,3 +151,11 @@
     padding-left: 24px;
     opacity: 50%;
 }
+
+.tree :target>details>summary,
+.tree :target>div {
+    border-bottom: 1px dashed rgba(0, 0, 0, 30%);
+    margin-bottom: -1px;
+    border-bottom-left-radius: 0;
+    border-bottom-right-radius: 0;
+}

static/js/tree.js

@@ -66,3 +66,23 @@ class LinkedBranch extends HTMLLIElement {
 }
 
 customElements.define("th-linked-branch", LinkedBranch, { extends: "li" });
+
+function expandDetailsRecursively(element) {
+    while (element && element.tagName != "MAIN") {
+        if (element.tagName == "DETAILS") {
+            element.open = true;
+        }
+        element = element.parentElement;
+    }
+}
+
+// When you click on a link, and the destination is within a <details> that is not expanded,
+// expand the <details> recursively.
+window.addEventListener("popstate", _ => {
+    let element = document.getElementById(window.location.hash.substring(1));
+    if (element !== undefined) {
+        // If the element is already loaded on the page, we're good.
+        expandDetailsRecursively(element);
+        window.location.hash = window.location.hash;
+    }
+})