diff --git a/crates/ui-egui/src/theme.rs b/crates/ui-egui/src/theme.rs
index d35e5657..1315d320 100644
--- a/crates/ui-egui/src/theme.rs
+++ b/crates/ui-egui/src/theme.rs
@@ -350,4 +350,15 @@ mod tests {
         }
         assert!(!Tokens::for_brightness(Brightness::Light).dark);
     }
+
+    /// #1662: a slider's rail (`button_border`, see `widgets::slider`) stands out from the panel
+    /// in every brightness.
+    #[test]
+    fn slider_rails_show_on_every_panel() {
+        for b in [Brightness::Dark, Brightness::MediumDark, Brightness::MediumLight, Brightness::Light] {
+            let t = Tokens::for_brightness(b);
+            let gap = (i32::from(t.button_border.r()) - i32::from(t.panel.r())).abs();
+            assert!(gap >= 24, "{b:?}: rail {:?} on panel {:?}", t.button_border, t.panel);
+        }
+    }
 }
diff --git a/crates/ui-egui/src/widgets.rs b/crates/ui-egui/src/widgets.rs
index 5ce5723b..e03c4a96 100644
--- a/crates/ui-egui/src/widgets.rs
+++ b/crates/ui-egui/src/widgets.rs
@@ -1014,7 +1014,9 @@ pub fn slider(ui: &mut Ui, slider: egui::Slider<'_>) -> Response {
     let t = Tokens::get(ui.ctx());
     ui.scope(|ui| {
         let v = ui.visuals_mut();
-        v.widgets.inactive.bg_fill = t.input_border;
+        // The buttons' border shows against the panel in every brightness; the fields' border
+        // all but vanished on Medium Dark's panel (#1662).
+        v.widgets.inactive.bg_fill = t.button_border;
         v.selection.bg_fill = t.accent;
         ui.add(slider.trailing_fill(true))
     })