diff --git a/CONTEXT.md b/CONTEXT.md
index 78ef7ef..0e0a849 100644
--- a/CONTEXT.md
+++ b/CONTEXT.md
@@ -41,7 +41,7 @@ The Library check that enforces Required Groups for the Requesting user on ExApp
 _Avoid_: Nextcloud middleware, HaRP ACL, admin bypass, gating the top-menu bootstrap script
 
 **App navigation**:
-The tree of named items along the left of an ExApp page. The ExApp supplies the tree. The selected item is the page on display. It plays the same role as the navigation in Nextcloud Files. An ExApp that does not use App navigation shows its own page instead.
+The tree of named items along the left of an ExApp page. The ExApp supplies the tree. The selected item is the page on display. It plays the same role as the navigation in Nextcloud Files. On a screen at most 1024px wide the tree is hidden until the user opens it; choosing an item, pressing Escape, or clicking outside closes it again. An ExApp that does not use App navigation shows its own page instead.
 _Avoid_: Top Menu, sidebar, NcAppNavigation
 
 **Dialog**:
diff --git a/README.md b/README.md
index bd94320..9a65e0c 100644
--- a/README.md
+++ b/README.md
@@ -18,7 +18,7 @@ Import: `gitea.neitzel.de/konrad/go-nc-exapp` (package `gonexapp`).
 - **Groups** — Users and Groups reads: `UserGroups`, `GroupMembers`, `ListGroups` (no search/paging). Directory calls (`GroupMembers` / `ListGroups`) run as the Credentials user and need an admin or subadmin
 - **Access Gate** — optional Required Groups enforcement (`Wrap` + `Check`), English denied HTML for browsers (200 + `frame-ancestors 'self'`), positive membership cache; default skip for lifecycle paths and **`/js/`** top-menu scripts; env helpers for `REQUIRED_GROUPS` / `REQUIRED_GROUPS_CACHE_SECONDS`
 - **Top Menu visibility** — `TopMenuAdminRequired` helper for deploy env `TOP_MENU_ADMIN_REQUIRED` (`0` / `1` for AppAPI top-menu OCS)
-- **App navigation** — optional Files-style shell (`AppNavigation.Handler`). The ExApp supplies the tree, the page for each item, and an optional header. The selected item is the `item` query parameter (override with `SelectKey`). Other query parameters, including a Visit folder, are left in place. By default the shell loads the Nextcloud theme stylesheets, paints `--image-background`, and copies the surrounding page’s `data-theme-*` markers; set `DisableTheme` to skip the stylesheets. An item may set `Icon` to a same-origin image URL. `NextcloudIcons` names the core SVGs Nextcloud already serves (`NextcloudIcons.Folder`, `NextcloudIcons.Password`, and the rest). The shell includes the Dialog. Not mounting the handler keeps the ExApp’s own page. Lifecycle routes, HaRP startup, and Top Menu registration stay in the ExApp.
+- **App navigation** — optional Files-style shell (`AppNavigation.Handler`). The ExApp supplies the tree, the page for each item, and an optional header. The selected item is the `item` query parameter (override with `SelectKey`). Other query parameters, including a Visit folder, are left in place. By default the shell loads the Nextcloud theme stylesheets, paints `--image-background`, and copies the surrounding page’s `data-theme-*` markers; set `DisableTheme` to skip the stylesheets. An item may set `Icon` to a same-origin image URL. `NextcloudIcons` names the core SVGs Nextcloud already serves (`NextcloudIcons.Folder`, `NextcloudIcons.Password`, and the rest). At 1024px and below, the tree is hidden until the user opens it with the navigation button; choosing an item, pressing Escape, or clicking outside closes it. The shell includes the Dialog. Not mounting the handler keeps the ExApp’s own page. Lifecycle routes, HaRP startup, and Top Menu registration stay in the ExApp.
 - **Dialog** — `DialogHTML()` is the modal for a Message, a Confirm, or a Prompt. Insert it on a page the ExApp renders itself; App navigation already includes it. The page calls `exappDialog.message`, `exappDialog.confirm`, or `exappDialog.prompt` and waits for the choice. Fixed buttons are the English words OK and Cancel. The agreeing button’s word may be replaced. The choice stays in the page.
 
 **Excluded**
diff --git a/dialog_test.go b/dialog_test.go
index a8d7ec7..0f8a001 100644
--- a/dialog_test.go
+++ b/dialog_test.go
@@ -59,6 +59,7 @@ func dialogFixture() http.Handler {
 		},
 	}
 	mux.Handle("GET /shell", nav.Handler())
+	mux.Handle("GET /nav", sampleNavigation().Handler())
 	return mux
 }
 
diff --git a/navigation.go b/navigation.go
index 858a0fa..8778b1d 100644
--- a/navigation.go
+++ b/navigation.go
@@ -170,6 +170,7 @@ var shellTmpl = template.Must(template.New("shell").Parse(`<!DOCTYPE html>
 <html lang="en">
 <head>
 <meta charset="utf-8">
+<meta name="viewport" content="width=device-width, initial-scale=1">
 <title>{{.Title}}</title>
 {{if .Theme}}
 <link rel="stylesheet" href="/apps/theming/css/default.css">
@@ -219,7 +220,32 @@ var shellTmpl = template.Must(template.New("shell").Parse(`<!DOCTYPE html>
   }
   body { margin: 0; font: 15px/1.4 var(--font-face, system-ui, sans-serif); }
   #app-nav { display: flex; flex-direction: column; min-height: 100vh; background: transparent; }
-  #nav-header { padding: 8px 12px; border-bottom: 1px solid var(--color-border); }
+  #nav-header {
+    display: flex;
+    align-items: center;
+    gap: 4px;
+    padding: 8px 12px;
+    border-bottom: 1px solid var(--color-border);
+  }
+  #nav-header-text { flex: 1; min-width: 0; }
+  #nav-toggle {
+    display: none;
+    align-items: center;
+    justify-content: center;
+    width: 44px;
+    height: 44px;
+    margin: 0;
+    padding: 0;
+    border: 0;
+    flex: none;
+    background: transparent;
+    color: inherit;
+    cursor: pointer;
+    border-radius: var(--border-radius-element);
+  }
+  #nav-toggle:hover { background: var(--color-background-hover); }
+  #nav-toggle svg { width: 20px; height: 20px; }
+  #nav-backdrop { display: none; }
   #app-nav-body { display: flex; flex: 1; min-height: 0; }
   nav.app-navigation {
     width: var(--navigation-width, 300px);
@@ -294,14 +320,47 @@ var shellTmpl = template.Must(template.New("shell").Parse(`<!DOCTYPE html>
   li[data-expanded="false"] > .app-navigation-entry__children { display: none; }
   li[data-expanded="false"] button.fold svg { transform: rotate(-90deg); }
   #nav-missing { margin: 0 0 1rem; }
+  @media (max-width: 1024px) {
+    #nav-header {
+      position: sticky;
+      top: 0;
+      z-index: 2100;
+      background-color: var(--color-main-background);
+    }
+    #nav-toggle { display: flex; }
+    nav.app-navigation {
+      display: none;
+      position: fixed;
+      z-index: 2000;
+      top: var(--nav-header-offset, 0px);
+      bottom: 0;
+      inset-inline-start: 0;
+      width: min(var(--navigation-width, 300px), 85vw);
+    }
+    body.nav-open nav.app-navigation { display: block; }
+    body.nav-open #nav-backdrop {
+      display: block;
+      position: fixed;
+      z-index: 1990;
+      top: var(--nav-header-offset, 0px);
+      right: 0;
+      bottom: 0;
+      left: 0;
+      background: rgba(0, 0, 0, 0.45);
+    }
+  }
 </style>
 </head>
 <body data-selected="{{.Selected}}" data-address="{{.Address}}">
 {{.Dialog}}
 <div id="app-nav">
-  <div id="nav-header">{{.Header}}</div>
+  <div id="nav-header">
+    <button type="button" id="nav-toggle" aria-controls="app-navigation" aria-expanded="false" aria-label="Open navigation"><svg viewBox="0 0 24 24" aria-hidden="true"><path fill="currentColor" d="M3 6h18v2H3V6m0 5h18v2H3v-2m0 5h18v2H3v-2z"/></svg></button>
+    <div id="nav-header-text">{{.Header}}</div>
+  </div>
+  <div id="nav-backdrop"></div>
   <div id="app-nav-body">
-    <nav class="app-navigation" aria-label="App navigation">
+    <nav id="app-navigation" class="app-navigation" aria-label="App navigation">
       <ul class="app-navigation-list">{{template "items" .Items}}</ul>
     </nav>
     <main>
@@ -325,6 +384,36 @@ var shellTmpl = template.Must(template.New("shell").Parse(`<!DOCTYPE html>
       btn.setAttribute("aria-expanded", open ? "false" : "true");
     });
   });
+  var toggle = document.getElementById("nav-toggle");
+  var backdrop = document.getElementById("nav-backdrop");
+  function placeNav() {
+    var header = document.getElementById("nav-header");
+    if (!header) return;
+    document.documentElement.style.setProperty("--nav-header-offset", header.offsetHeight + "px");
+  }
+  function setNavOpen(open) {
+    placeNav();
+    document.body.classList.toggle("nav-open", open);
+    if (!toggle) return;
+    toggle.setAttribute("aria-expanded", open ? "true" : "false");
+    toggle.setAttribute("aria-label", open ? "Close navigation" : "Open navigation");
+  }
+  placeNav();
+  window.addEventListener("resize", placeNav);
+  var narrow = window.matchMedia("(max-width: 1024px)");
+  if (narrow.addEventListener) narrow.addEventListener("change", placeNav);
+  if (toggle) {
+    toggle.addEventListener("click", function () {
+      setNavOpen(!document.body.classList.contains("nav-open"));
+    });
+  }
+  if (backdrop) backdrop.addEventListener("click", function () { setNavOpen(false); });
+  document.addEventListener("keydown", function (e) {
+    if (e.key !== "Escape") return;
+    var dialog = document.getElementById("exapp-dialog");
+    if (dialog && dialog.open) return;
+    setNavOpen(false);
+  });
 })();
 </script>
 </body>
diff --git a/navigation_test.go b/navigation_test.go
index a8f513f..efb20ba 100644
--- a/navigation_test.go
+++ b/navigation_test.go
@@ -8,6 +8,9 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/chromedp/chromedp"
+	"github.com/chromedp/chromedp/kb"
+
 	"gitea.neitzel.de/konrad/go-nc-exapp"
 )
 
@@ -201,3 +204,67 @@ func TestAppNavigationHeaderPrecedesTree(t *testing.T) {
 		t.Fatalf("header %d tree %d in %s", header, tree, body)
 	}
 }
+
+func TestAppNavigationOffersNarrowScreenToggle(t *testing.T) {
+	body := navBody(t, "/")
+	for _, need := range []string{
+		`<meta name="viewport" content="width=device-width, initial-scale=1">`,
+		`id="nav-toggle"`,
+		`aria-controls="app-navigation"`,
+		`aria-expanded="false"`,
+		`aria-label="Open navigation"`,
+		`id="nav-backdrop"`,
+		`id="app-navigation"`,
+		`max-width: 1024px`,
+	} {
+		if !strings.Contains(body, need) {
+			t.Errorf("missing %s", need)
+		}
+	}
+}
+
+// navLayoutJS reports how App navigation is laid out: "wide", "closed", or "open".
+const navLayoutJS = `(() => {
+  const nav = document.querySelector("nav.app-navigation");
+  const btn = document.getElementById("nav-toggle");
+  const narrow = window.matchMedia("(max-width: 1024px)").matches;
+  const box = nav.getBoundingClientRect();
+  const navShown = getComputedStyle(nav).display !== "none" && box.width > 0 && box.left < window.innerWidth && box.right > 0;
+  const btnShown = getComputedStyle(btn).display !== "none";
+  const expanded = btn.getAttribute("aria-expanded") === "true";
+  if (!narrow && navShown && !btnShown && !expanded) return "wide";
+  if (narrow && !navShown && btnShown && !expanded) return "closed";
+  if (narrow && navShown && btnShown && expanded) return "open";
+  return "narrow=" + narrow + " nav=" + navShown + " btn=" + btnShown + " expanded=" + expanded + " width=" + window.innerWidth;
+})()`
+
+func TestAppNavigationWideScreenKeepsTheTreeVisible(t *testing.T) {
+	drive(t, "/nav",
+		chromedp.EmulateViewport(1280, 800),
+		waitJS(navLayoutJS, "wide", false),
+	)
+}
+
+func TestAppNavigationNarrowScreenOpensTheTreeOnDemand(t *testing.T) {
+	drive(t, "/nav",
+		chromedp.EmulateViewport(390, 800),
+		waitJS(navLayoutJS, "closed", false),
+		chromedp.Click("#nav-toggle", chromedp.ByQuery),
+		waitJS(navLayoutJS, "open", false),
+		chromedp.Click("#nav-toggle", chromedp.ByQuery),
+		waitJS(navLayoutJS, "closed", false),
+		chromedp.Click("#nav-toggle", chromedp.ByQuery),
+		waitJS(navLayoutJS, "open", false),
+		chromedp.MouseClickXY(370, 400),
+		waitJS(navLayoutJS, "closed", false),
+		chromedp.Click("#nav-toggle", chromedp.ByQuery),
+		waitJS(navLayoutJS, "open", false),
+		chromedp.KeyEvent(kb.Escape),
+		waitJS(navLayoutJS, "closed", false),
+		chromedp.Click("#nav-toggle", chromedp.ByQuery),
+		waitJS(navLayoutJS, "open", false),
+		chromedp.Click(`a.app-navigation-entry-link[href*="item=keys"]`, chromedp.ByQuery),
+		waitJS(`document.querySelector("main").textContent`, "keys-page", true),
+		waitJS(navLayoutJS, "closed", false),
+	)
+}