Fix fade in.

src/slide/s4_automata.rs

@@ -149,14 +149,17 @@ impl Slide for Automata {
         if let Some(rules_fade) = rules_fade {
             fade_in(ui, rules_fade, |ui| {
                 Window::new("conway_rules")
-                    .frame(Frame::window(&ui.ctx().style()))
+                    .frame(Frame::window(&ui.style()))
                     .anchor(Align2::CENTER_CENTER, Vec2::new(HORIZONTAL_OFFSET, 0.0))
                     .title_bar(false)
                     .resizable(false)
                     .show(ui.ctx(), |ui| {
-                        ui.label(" ⏵ Cells with fewer than two neighbors die");
-                        ui.label(" ⏵ Cells with more than three neighbors die");
-                        ui.label(" ⏵ Cells with three neighbors become alive");
+                        // Nested fade in since fade doesn't propagate from [`Window`] to children.
+                        fade_in(ui, rules_fade, |ui| {
+                            ui.label(" ⏵ Cells with fewer than two neighbors die");
+                            ui.label(" ⏵ Cells with more than three neighbors die");
+                            ui.label(" ⏵ Cells with three neighbors become alive");
+                        })
                     });
             });
         }