Nested Layouts

[Markkaz]

I'm using EGUI as a GUI framework for the menu's in a game. Using EGUI for the main menu is pretty straight foward. However, I get stuck when trying to setup a settings menu.
My problem is that I want to nest layouts. My overall menu needs to be centered, but in the settings menu I'm trying to get my comboboxes, etc and labels horizontally aligned.
For now I have the following code:

fn settings_menu(mut contexts: EguiContexts) {
    let ctx = contexts.ctx_mut();

    let mut diffulty = Difficulty::Easy;

    egui::CentralPanel::default().show(ctx, |ui| {
        ui.vertical_centered(|ui| {
            ui.add_space(200.);

            ui.heading(egui::RichText::new("Settings")
                .size(48.)
                .color(egui::Color32::WHITE)
                .strong());
            ui.add_space(40.);

            ui.horizontal(|ui| {
                ui.label("Difficulty: ");
                ui.selectable_value(&mut diffulty, Difficulty::Easy, "Easy");
                ui.selectable_value(&mut diffulty, Difficulty::Difficult, "Difficult");
                ui.selectable_value(&mut diffulty, Difficulty::Impossible, "Impossible");
            });

            ui.add_space(10.);

            ui.add_sized(
                egui::Vec2::new(200., 50.),
                egui::Button::new(
                    egui::RichText::new("Back")
                        .size(24.)
                        .color(egui::Color32::WHITE)
                )
            );

            ui.add_space(10.);
        });
    });
}

The header and the back button get nicely centered. However, the selectable_values are moved all the way to the left of the screen. And I cannot find a way to properly align them.

PS: I tried the same code on both Mac and Windows, same result.

[Markkaz]

Ok, after a night of trying different things I found a solution. I force the ui.horizontal to a fixed with and then I can center it:

let layout = egui::Layout::centered_and_justified(egui::Direction::LeftToRight);
            ui.allocate_ui_with_layout([600., 50.].into(), layout, |ui| {
                ui.horizontal(|ui| {
                    ui.label(egui::RichText::new("Difficulty: ").size(24.).color(egui::Color32::WHITE));

                    if ui.add_sized(
                        egui::Vec2::new(200., 50.),
                        egui::SelectableLabel::new(
                            difficulty.0 == Difficulty::Easy,
                            egui::RichText::new("Easy").size(24.).color(egui::Color32::WHITE)
                        )
                    ).clicked() {
                        difficulty.0 = Difficulty::Easy;
                    }

                    if ui.add_sized(
                        egui::Vec2::new(200., 50.),
                        egui::SelectableLabel::new(
                            difficulty.0 == Difficulty::Difficult,
                            egui::RichText::new("Difficult").size(24.).color(egui::Color32::WHITE)
                        )
                    ).clicked() {
                        difficulty.0 = Difficulty::Difficult;
                    }

                    if ui.add_sized(
                        egui::Vec2::new(200., 50.),
                        egui::SelectableLabel::new(
                            difficulty.0 == Difficulty::Impossible,
                            egui::RichText::new("Impossible").size(24.).color(egui::Color32::WHITE)
                        )
                    ).clicked() {
                        difficulty.0 = Difficulty::Impossible;
                    }
                });
            });