diff --git a/crates/snowbound/src/main.rs b/crates/snowbound/src/main.rs
index e99d7e7936ea953c58d4f922901d22ccd1d9fd13..d23ba0148df95a0c43d3e085b2d375d21ea4d553 100644
--- a/crates/snowbound/src/main.rs
+++ b/crates/snowbound/src/main.rs
@@ -1722,9 +1722,9 @@ impl State {
         );
         if !self.temporary {
             // Past the row's padding, the frame's corner and the first tab's shadow, the tabs'
-            // outlines start where Back and Forward end, and on the left the notebook button's
-            // square after them; that room shrinks on the sidebar's easing, as they move into
-            // its header, so the tabs ease with it.
+            // outlines start where Back and Forward end, after the notebook button's square on
+            // the left; that room shrinks on the sidebar's easing, as they move into its
+            // header, so the tabs ease with it.
             let room = sidebar::NAV + TAB_ROW - FRAME - self.rounding() - ui::SHADOW[0];
             let room = if self.navigation_bar_right {
                 room - TAB_ROW
diff --git a/crates/snowbound/src/sidebar.rs b/crates/snowbound/src/sidebar.rs
index 43ecc29b3c0d091638772ea5e7329472b8e1684e..0a6cd81520af16766cf5eb5f22127f4cbc4b86ae 100644
--- a/crates/snowbound/src/sidebar.rs
+++ b/crates/snowbound/src/sidebar.rs
@@ -196,10 +196,17 @@ fn sidebar(
             ..Spec::default()
         },
     );
+    // Room for what floats over the header's start: the notebook button's icon, and on the
+    // left Back and Forward after it.
+    let start = if right {
+        ICON
+    } else {
+        (ICON + RAIL) / 2.0 + NAV - ROW_PAD
+    };
     ui.leaf(
         "icon",
         Spec {
-            size: [px(ICON), px(ui::shell::TOOL)],
+            size: [px(start), px(ui::shell::TOOL)],
             ..Spec::default()
         },
     );
@@ -212,15 +219,16 @@ fn sidebar(
             ..Spec::default()
         },
     );
-    // Room for what floats over the header's end.
-    let end = if right { RAIL } else { NAV + MARGIN };
-    ui.leaf(
-        "end",
-        Spec {
-            size: [px(end - MARGIN - 2.0 * ROW_PAD), px(1.0)],
-            ..Spec::default()
-        },
-    );
+    // Room for the notebook button floating over the header's end.
+    if right {
+        ui.leaf(
+            "end",
+            Spec {
+                size: [px(RAIL - MARGIN - 2.0 * ROW_PAD), px(1.0)],
+                ..Spec::default()
+            },
+        );
+    }
     ui.close();
     if !rows {
         return;
@@ -970,10 +978,10 @@ impl crate::State {
         }
     }
 
-    /// Back, Forward and the notebook button, floating at the body's corner over the section
-    /// tabs' row, `height` tall as it eases. While the sidebar, `width` wide as it eases, is
-    /// open on the left, the notebook button closes it from its header's icon, and Back and
-    /// Forward ride its end.
+    /// The notebook button, then Back and Forward, floating at the body's corner over the
+    /// section tabs' row, `height` tall as it eases. While the sidebar, `width` wide as it
+    /// eases, is open on the left, the notebook button closes it from its header's icon, Back
+    /// and Forward after it.
     pub(crate) fn sidebar_button(&mut self, height: f32, width: f32) {
         use crate::commands::{Choice, Id as Cmd};
         if self.temporary {
@@ -987,9 +995,8 @@ impl crate::State {
                 .map_or(0.0, |[left, _, right, _]| right - left - RAIL);
             (0.0, edge)
         } else {
-            let open = MARGIN + ROW_PAD - (RAIL - ICON) / 2.0;
-            let toggle = NAV + (open - NAV) * width / WIDTH;
-            ((width - NAV - MARGIN).max(0.0), toggle)
+            let toggle = (MARGIN + ROW_PAD - (RAIL - ICON) / 2.0) * width / WIDTH;
+            (toggle + RAIL, toggle)
         };
         let pad = [
             (RAIL - ui::shell::TOOL) / 2.0,