From a19fd7b780de57185191e4c1a92c5343debf68b0 Mon Sep 17 00:00:00 2001
From: Emil Ernerfeldt <emilernerfeldt@gmail.com>
Date: Wed, 3 Feb 2021 01:08:23 +0100
Subject: [PATCH] Add light mode

---
 egui/src/containers/scroll_area.rs          |   2 +-
 egui/src/grid.rs                            |  14 +-
 egui/src/menu.rs                            |   4 +-
 egui/src/style.rs                           | 221 ++++++++++++++++----
 egui/src/ui.rs                              |  10 +-
 egui/src/widgets/slider.rs                  |   2 +-
 egui/src/widgets/text_edit.rs               |   4 +-
 egui_demo_lib/src/apps/demo/demo_windows.rs |   7 +
 egui_demo_lib/src/apps/fractal_clock.rs     |   1 -
 egui_demo_lib/src/frame_history.rs          |   9 +-
 egui_demo_lib/src/wrap_app.rs               |  11 +
 epaint/src/shadow.rs                        |  12 +-
 12 files changed, 230 insertions(+), 67 deletions(-)

diff --git a/egui/src/containers/scroll_area.rs b/egui/src/containers/scroll_area.rs
index 5c187b3e..e9e44f6e 100644
--- a/egui/src/containers/scroll_area.rs
+++ b/egui/src/containers/scroll_area.rs
@@ -331,7 +331,7 @@ impl Prepared {
             ui.painter().add(paint::Shape::Rect {
                 rect: outer_scroll_rect,
                 corner_radius,
-                fill: ui.visuals().dark_bg_color,
+                fill: ui.visuals().extreme_bg_color,
                 stroke: Default::default(),
                 // fill: visuals.bg_fill,
                 // stroke: visuals.bg_stroke,
diff --git a/egui/src/grid.rs b/egui/src/grid.rs
index 97c4547a..c0772d1e 100644
--- a/egui/src/grid.rs
+++ b/egui/src/grid.rs
@@ -38,6 +38,7 @@ impl State {
 
 pub(crate) struct GridLayout {
     ctx: CtxRef,
+    style: std::sync::Arc<Style>,
     id: Id,
 
     /// State previous frame (if any).
@@ -61,6 +62,7 @@ impl GridLayout {
 
         Self {
             ctx: ui.ctx().clone(),
+            style: ui.style().clone(),
             id,
             prev_state,
             curr_state: State::default(),
@@ -125,8 +127,8 @@ impl GridLayout {
     }
 
     pub(crate) fn advance(&mut self, cursor: &mut Pos2, frame_rect: Rect, widget_rect: Rect) {
-        let debug_expand_width = self.ctx.style().visuals.debug_expand_width;
-        let debug_expand_height = self.ctx.style().visuals.debug_expand_height;
+        let debug_expand_width = self.style.visuals.debug_expand_width;
+        let debug_expand_height = self.style.visuals.debug_expand_height;
         if debug_expand_width || debug_expand_height {
             let rect = widget_rect;
             let too_wide = rect.width() > self.prev_col_width(self.col);
@@ -173,8 +175,12 @@ impl GridLayout {
                 let rect = Rect::from_min_size(*cursor, size);
                 let rect = rect.expand2(0.5 * self.spacing.y * Vec2::Y);
                 let rect = rect.expand2(2.0 * Vec2::X); // HACK: just looks better with some spacing on the sides
-                let color = Rgba::from_white_alpha(0.0075);
-                // let color = Rgba::from_black_alpha(0.2);
+
+                let color = if self.style.visuals.dark_mode {
+                    Rgba::from_white_alpha(0.0075)
+                } else {
+                    Rgba::from_black_alpha(0.075)
+                };
                 painter.rect_filled(rect, 2.0, color);
             }
         }
diff --git a/egui/src/menu.rs b/egui/src/menu.rs
index ebe7c5b3..d64ad056 100644
--- a/egui/src/menu.rs
+++ b/egui/src/menu.rs
@@ -42,7 +42,7 @@ impl BarState {
 /// In the latter case you may want to wrap it in `Frame`.
 pub fn bar<R>(ui: &mut Ui, add_contents: impl FnOnce(&mut Ui) -> R) -> (R, Response) {
     ui.horizontal(|ui| {
-        let mut style = ui.style().clone();
+        let mut style = (**ui.style()).clone();
         style.spacing.button_padding = vec2(2.0, 0.0);
         // style.visuals.widgets.active.bg_fill = Color32::TRANSPARENT;
         style.visuals.widgets.active.bg_stroke = Stroke::none();
@@ -102,7 +102,7 @@ fn menu_impl<'c>(
 
         area.show(ui.ctx(), |ui| {
             frame.show(ui, |ui| {
-                let mut style = ui.style().clone();
+                let mut style = (**ui.style()).clone();
                 style.spacing.button_padding = vec2(2.0, 0.0);
                 // style.visuals.widgets.active.bg_fill = Color32::TRANSPARENT;
                 style.visuals.widgets.active.bg_stroke = Stroke::none();
diff --git a/egui/src/style.rs b/egui/src/style.rs
index 40d79b9c..5c427e6e 100644
--- a/egui/src/style.rs
+++ b/egui/src/style.rs
@@ -111,6 +111,10 @@ pub struct Interaction {
 #[cfg_attr(feature = "persistence", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "persistence", serde(default))]
 pub struct Visuals {
+    /// If true, the visuals are overall dark with light text.
+    /// If false, the visuals are overall light with dark text.
+    pub dark_mode: bool,
+
     /// Override default text color for all text.
     ///
     /// This is great for setting the color of text for any widget.
@@ -131,9 +135,10 @@ pub struct Visuals {
 
     pub selection: Selection,
 
-    /// e.g. the background of the slider or text edit,
-    /// needs to look different from other interactive stuff.
-    pub dark_bg_color: Color32, // TODO: remove, rename, or clarify what it is for
+    /// Very dark or light color (for corresponding theme).
+    /// Used as the background of text edits, scroll bars and others things
+    /// that needs to look different from other interactive stuff.
+    pub extreme_bg_color: Color32,
 
     /// The color used for `Hyperlink`,
     pub hyperlink_color: Color32,
@@ -286,17 +291,18 @@ impl Default for Interaction {
     }
 }
 
-impl Default for Visuals {
-    fn default() -> Self {
+impl Visuals {
+    pub fn dark() -> Self {
         Self {
+            dark_mode: true,
             override_text_color: None,
-            widgets: Default::default(),
-            selection: Default::default(),
-            dark_bg_color: Color32::from_gray(10),
+            widgets: Widgets::default(),
+            selection: Selection::default(),
+            extreme_bg_color: Color32::from_gray(10),
             hyperlink_color: Color32::from_rgb(90, 170, 255),
             code_bg_color: Color32::from_gray(64),
             window_corner_radius: 10.0,
-            window_shadow: Shadow::big(),
+            window_shadow: Shadow::big_dark(),
             resize_corner_size: 12.0,
             text_cursor_width: 2.0,
             clip_rect_margin: 3.0, // should be at least half the size of the widest frame stroke + max WidgetVisuals::expansion
@@ -305,10 +311,29 @@ impl Default for Visuals {
             debug_resize: false,
         }
     }
+
+    pub fn light() -> Self {
+        Self {
+            dark_mode: false,
+            widgets: Widgets::light(),
+            selection: Selection::light(),
+            extreme_bg_color: Color32::from_gray(235), // TODO: rename
+            hyperlink_color: Color32::from_rgb(0, 133, 218),
+            code_bg_color: Color32::from_gray(200),
+            window_shadow: Shadow::big_light(),
+            ..Self::dark()
+        }
+    }
 }
 
-impl Default for Selection {
+impl Default for Visuals {
     fn default() -> Self {
+        Self::dark()
+    }
+}
+
+impl Selection {
+    fn dark() -> Self {
         Self {
             bg_fill: Rgba::from_rgb(0.0, 0.5, 1.0)
                 .additive()
@@ -317,53 +342,106 @@ impl Default for Selection {
             stroke: Stroke::new(1.0, Rgba::from_rgb(0.3, 0.6, 1.0)),
         }
     }
+    fn light() -> Self {
+        Self {
+            bg_fill: Rgba::from_rgb(0.0, 0.5, 1.0).multiply(0.5).into(),
+            stroke: Stroke::new(1.0, Rgba::from_rgb(0.3, 0.6, 1.0)),
+        }
+    }
 }
 
-impl Default for Widgets {
+impl Default for Selection {
     fn default() -> Self {
+        Self::dark()
+    }
+}
+
+impl Widgets {
+    pub fn dark() -> Self {
         Self {
             noninteractive: WidgetVisuals {
                 bg_stroke: Stroke::new(1.0, Color32::from_gray(65)), // window outline
                 bg_fill: Color32::from_gray(30),                     // window background
-                corner_radius: 4.0,
-
                 fg_stroke: Stroke::new(1.0, Color32::from_gray(160)), // text color
+                corner_radius: 4.0,
                 expansion: 0.0,
             },
             disabled: WidgetVisuals {
                 bg_fill: Color32::from_gray(40), // Should look grayed out
                 bg_stroke: Stroke::new(1.0, Color32::from_gray(70)),
-                corner_radius: 4.0,
-
                 fg_stroke: Stroke::new(1.0, Color32::from_gray(140)), // Should look grayed out
+                corner_radius: 4.0,
                 expansion: 0.0,
             },
             inactive: WidgetVisuals {
                 bg_fill: Color32::from_gray(70),
                 bg_stroke: Default::default(),
-                corner_radius: 4.0,
-
                 fg_stroke: Stroke::new(1.0, Color32::from_gray(200)), // Should NOT look grayed out!
+                corner_radius: 4.0,
                 expansion: 0.0,
             },
             hovered: WidgetVisuals {
                 bg_fill: Color32::from_gray(80),
                 bg_stroke: Stroke::new(1.0, Color32::from_gray(150)), // e.g. hover over window edge or button
-                corner_radius: 4.0,
-
                 fg_stroke: Stroke::new(1.5, Color32::from_gray(240)),
+                corner_radius: 4.0,
                 expansion: 1.0,
             },
             active: WidgetVisuals {
                 bg_fill: Color32::from_gray(90),
                 bg_stroke: Stroke::new(1.0, Color32::WHITE),
-                corner_radius: 4.0,
-
                 fg_stroke: Stroke::new(2.0, Color32::WHITE),
+                corner_radius: 4.0,
                 expansion: 2.0,
             },
         }
     }
+
+    pub fn light() -> Self {
+        Self {
+            noninteractive: WidgetVisuals {
+                bg_stroke: Stroke::new(1.0, Color32::from_gray(180)), // window outline
+                bg_fill: Color32::from_gray(220),                     // window background
+                fg_stroke: Stroke::new(1.0, Color32::from_gray(70)),  // text color
+                corner_radius: 4.0,
+                expansion: 0.0,
+            },
+            disabled: WidgetVisuals {
+                bg_fill: Color32::from_gray(215), // Should look grayed out
+                bg_stroke: Stroke::new(1.0, Color32::from_gray(185)),
+                fg_stroke: Stroke::new(1.0, Color32::from_gray(115)), // Should look grayed out
+                corner_radius: 4.0,
+                expansion: 0.0,
+            },
+            inactive: WidgetVisuals {
+                bg_fill: Color32::from_gray(195),
+                bg_stroke: Default::default(),
+                fg_stroke: Stroke::new(1.0, Color32::from_gray(55)), // Should NOT look grayed out!
+                corner_radius: 4.0,
+                expansion: 0.0,
+            },
+            hovered: WidgetVisuals {
+                bg_fill: Color32::from_gray(175),
+                bg_stroke: Stroke::new(1.0, Color32::from_gray(105)), // e.g. hover over window edge or button
+                fg_stroke: Stroke::new(2.0, Color32::BLACK),
+                corner_radius: 4.0,
+                expansion: 1.0,
+            },
+            active: WidgetVisuals {
+                bg_fill: Color32::from_gray(165),
+                bg_stroke: Stroke::new(1.0, Color32::BLACK),
+                fg_stroke: Stroke::new(2.0, Color32::BLACK),
+                corner_radius: 4.0,
+                expansion: 2.0,
+            },
+        }
+    }
+}
+
+impl Default for Widgets {
+    fn default() -> Self {
+        Self::dark()
+    }
 }
 
 // ----------------------------------------------------------------------------
@@ -372,8 +450,6 @@ use crate::{widgets::*, Ui};
 
 impl Style {
     pub fn ui(&mut self, ui: &mut crate::Ui) {
-        crate::reset_button(ui, self);
-
         let Self {
             body_text_style,
             spacing,
@@ -381,6 +457,9 @@ impl Style {
             visuals,
             animation_time,
         } = self;
+
+        visuals.light_dark_radio_buttons(ui);
+
         ui.horizontal(|ui| {
             ui.label("Default text style:");
             for &value in &[TextStyle::Body, TextStyle::Monospace] {
@@ -391,13 +470,13 @@ impl Style {
         ui.collapsing("☝ Interaction", |ui| interaction.ui(ui));
         ui.collapsing("🎨 Visuals", |ui| visuals.ui(ui));
         ui.add(Slider::f32(animation_time, 0.0..=1.0).text("animation_time"));
+
+        ui.vertical_centered(|ui| reset_button(ui, self));
     }
 }
 
 impl Spacing {
     pub fn ui(&mut self, ui: &mut crate::Ui) {
-        crate::reset_button(ui, self);
-
         let Self {
             item_spacing,
             window_padding,
@@ -422,13 +501,13 @@ impl Spacing {
         ui.add(Slider::f32(icon_width, 0.0..=60.0).text("icon_width"));
         ui.add(Slider::f32(icon_spacing, 0.0..=10.0).text("icon_spacing"));
         ui.add(Slider::f32(tooltip_width, 0.0..=10.0).text("tooltip_width"));
+
+        ui.vertical_centered(|ui| reset_button(ui, self));
     }
 }
 
 impl Interaction {
     pub fn ui(&mut self, ui: &mut crate::Ui) {
-        crate::reset_button(ui, self);
-
         let Self {
             resize_grab_radius_side,
             resize_grab_radius_corner,
@@ -437,13 +516,13 @@ impl Interaction {
         ui.add(
             Slider::f32(resize_grab_radius_corner, 0.0..=20.0).text("resize_grab_radius_corner"),
         );
+
+        ui.vertical_centered(|ui| reset_button(ui, self));
     }
 }
 
 impl Widgets {
     pub fn ui(&mut self, ui: &mut crate::Ui) {
-        crate::reset_button(ui, self);
-
         let Self {
             active,
             hovered,
@@ -472,6 +551,8 @@ impl Widgets {
             ui.label("The style of a widget as you are clicking or dragging it.");
             active.ui(ui)
         });
+
+        ui.vertical_centered(|ui| reset_button(ui, self));
     }
 }
 
@@ -503,14 +584,47 @@ impl WidgetVisuals {
 }
 
 impl Visuals {
-    pub fn ui(&mut self, ui: &mut crate::Ui) {
-        crate::reset_button(ui, self);
+    /// Show radio-buttons to switch between light and dark mode.
+    pub fn light_dark_radio_buttons(&mut self, ui: &mut crate::Ui) {
+        ui.group(|ui| {
+            ui.horizontal(|ui| {
+                ui.radio_value(self, Self::light(), "☀ Light");
+                ui.radio_value(self, Self::dark(), "🌙 Dark");
+            });
+        });
+    }
 
+    /// Show small toggle-button for light and dark mode.
+    #[must_use]
+    pub fn light_dark_small_toggle_button(&self, ui: &mut crate::Ui) -> Option<Self> {
+        #![allow(clippy::collapsible_if)]
+        if self.dark_mode {
+            if ui
+                .add(Button::new("☀").frame(false))
+                .on_hover_text("Switch to light mode")
+                .clicked()
+            {
+                return Some(Self::light());
+            }
+        } else {
+            if ui
+                .add(Button::new("🌙").frame(false))
+                .on_hover_text("Switch to dark mode")
+                .clicked()
+            {
+                return Some(Self::dark());
+            }
+        }
+        None
+    }
+
+    pub fn ui(&mut self, ui: &mut crate::Ui) {
         let Self {
+            dark_mode: _,
             override_text_color: _,
             widgets,
             selection,
-            dark_bg_color,
+            extreme_bg_color,
             hyperlink_color,
             code_bg_color,
             window_corner_radius,
@@ -525,25 +639,42 @@ impl Visuals {
 
         ui.collapsing("widgets", |ui| widgets.ui(ui));
         ui.collapsing("selection", |ui| selection.ui(ui));
-        ui_color(ui, dark_bg_color, "dark_bg_color");
+
+        ui.group(|ui| {
+            ui.label("Window");
+            // Common shortcuts
+            ui_color(ui, &mut widgets.noninteractive.bg_fill, "Fill");
+            stroke_ui(ui, &mut widgets.noninteractive.bg_stroke, "Outline");
+            ui.add(Slider::f32(window_corner_radius, 0.0..=20.0).text("Corner Radius"));
+            shadow_ui(ui, window_shadow, "Shadow");
+        });
+        ui_color(
+            ui,
+            &mut widgets.noninteractive.fg_stroke.color,
+            "Text color",
+        );
+
+        ui_color(ui, extreme_bg_color, "extreme_bg_color");
         ui_color(ui, hyperlink_color, "hyperlink_color");
         ui_color(ui, code_bg_color, "code_bg_color");
-        ui.add(Slider::f32(window_corner_radius, 0.0..=20.0).text("window_corner_radius"));
-        shadow_ui(ui, window_shadow, "Window shadow:");
         ui.add(Slider::f32(resize_corner_size, 0.0..=20.0).text("resize_corner_size"));
         ui.add(Slider::f32(text_cursor_width, 0.0..=2.0).text("text_cursor_width"));
         ui.add(Slider::f32(clip_rect_margin, 0.0..=20.0).text("clip_rect_margin"));
 
-        ui.label("DEBUG:");
-        ui.checkbox(
-            debug_expand_width,
-            "Show which widgets make their parent wider",
-        );
-        ui.checkbox(
-            debug_expand_height,
-            "Show which widgets make their parent higher",
-        );
-        ui.checkbox(debug_resize, "Debug Resize");
+        ui.group(|ui| {
+            ui.label("DEBUG:");
+            ui.checkbox(
+                debug_expand_width,
+                "Show which widgets make their parent wider",
+            );
+            ui.checkbox(
+                debug_expand_height,
+                "Show which widgets make their parent higher",
+            );
+            ui.checkbox(debug_resize, "Debug Resize");
+        });
+
+        ui.vertical_centered(|ui| reset_button(ui, self));
     }
 }
 
diff --git a/egui/src/ui.rs b/egui/src/ui.rs
index 95eb46be..d3178acd 100644
--- a/egui/src/ui.rs
+++ b/egui/src/ui.rs
@@ -1,6 +1,6 @@
 // #![warn(missing_docs)]
 
-use std::{hash::Hash, sync::Arc};
+use std::hash::Hash;
 
 use crate::{
     color::*, containers::*, layout::*, mutex::MutexGuard, paint::text::Fonts, placer::Placer,
@@ -42,7 +42,7 @@ pub struct Ui {
     /// The `Style` (visuals, spacing, etc) of this ui.
     /// Commonly many `Ui`:s share the same `Style`.
     /// The `Ui` implements copy-on-write for this.
-    style: Arc<Style>,
+    style: std::sync::Arc<Style>,
 
     /// Handles the `Ui` size and the placement of new widgets.
     placer: Placer,
@@ -93,18 +93,18 @@ impl Ui {
     }
 
     /// Style options for this `Ui` and its children.
-    pub fn style(&self) -> &Style {
+    pub fn style(&self) -> &std::sync::Arc<Style> {
         &self.style
     }
 
     /// Mutably borrow internal `Style`.
     /// Changes apply to this `Ui` and its subsequent children.
     pub fn style_mut(&mut self) -> &mut Style {
-        Arc::make_mut(&mut self.style) // clone-on-write
+        std::sync::Arc::make_mut(&mut self.style) // clone-on-write
     }
 
     /// Changes apply to this `Ui` and its subsequent children.
-    pub fn set_style(&mut self, style: impl Into<Arc<Style>>) {
+    pub fn set_style(&mut self, style: impl Into<std::sync::Arc<Style>>) {
         self.style = style.into();
     }
 
diff --git a/egui/src/widgets/slider.rs b/egui/src/widgets/slider.rs
index 6c6ebc82..1610ca62 100644
--- a/egui/src/widgets/slider.rs
+++ b/egui/src/widgets/slider.rs
@@ -306,7 +306,7 @@ impl<'a> Slider<'a> {
 
                 fill: ui.visuals().widgets.inactive.bg_fill,
                 // fill: visuals.bg_fill,
-                // fill: ui.visuals().dark_bg_color,
+                // fill: ui.visuals().extreme_bg_color,
                 stroke: Default::default(),
                 // stroke: visuals.bg_stroke,
                 // stroke: ui.visuals().widgets.inactive.bg_stroke,
diff --git a/egui/src/widgets/text_edit.rs b/egui/src/widgets/text_edit.rs
index 6564826f..43429a74 100644
--- a/egui/src/widgets/text_edit.rs
+++ b/egui/src/widgets/text_edit.rs
@@ -245,14 +245,14 @@ impl<'t> Widget for TextEdit<'t> {
                     rect: frame_rect,
                     corner_radius: visuals.corner_radius,
                     // fill: ui.visuals().selection.bg_fill,
-                    fill: ui.visuals().dark_bg_color,
+                    fill: ui.visuals().extreme_bg_color,
                     stroke: ui.visuals().selection.stroke,
                 }
             } else {
                 Shape::Rect {
                     rect: frame_rect,
                     corner_radius: visuals.corner_radius,
-                    fill: ui.visuals().dark_bg_color,
+                    fill: ui.visuals().extreme_bg_color,
                     stroke: visuals.bg_stroke, // TODO: we want to show something here, or a text-edit field doesn't "pop".
                 }
             };
diff --git a/egui_demo_lib/src/apps/demo/demo_windows.rs b/egui_demo_lib/src/apps/demo/demo_windows.rs
index 08f48a9a..2405bf98 100644
--- a/egui_demo_lib/src/apps/demo/demo_windows.rs
+++ b/egui_demo_lib/src/apps/demo/demo_windows.rs
@@ -101,6 +101,13 @@ impl DemoWindows {
             show_menu_bar(ui);
         });
 
+        // Just get a background to put the windows on instead of using whatever the clear color is
+        let frame = egui::Frame {
+            fill: ctx.style().visuals.extreme_bg_color,
+            ..egui::Frame::none()
+        };
+        egui::CentralPanel::default().frame(frame).show(ctx, |_| {});
+
         self.windows(ctx);
     }
 
diff --git a/egui_demo_lib/src/apps/fractal_clock.rs b/egui_demo_lib/src/apps/fractal_clock.rs
index 8a7b8f90..c158f96d 100644
--- a/egui_demo_lib/src/apps/fractal_clock.rs
+++ b/egui_demo_lib/src/apps/fractal_clock.rs
@@ -59,7 +59,6 @@ impl FractalClock {
         ui.expand_to_include_rect(painter.clip_rect());
 
         Frame::popup(ui.style())
-            .fill(Rgba::from_luminance_alpha(0.02, 0.5).into())
             .stroke(Stroke::none())
             .show(ui, |ui| {
                 ui.set_max_width(270.0);
diff --git a/egui_demo_lib/src/frame_history.rs b/egui_demo_lib/src/frame_history.rs
index 8b732366..0939e0cf 100644
--- a/egui_demo_lib/src/frame_history.rs
+++ b/egui_demo_lib/src/frame_history.rs
@@ -72,12 +72,13 @@ impl FrameHistory {
         let mut shapes = vec![Shape::Rect {
             rect,
             corner_radius: style.corner_radius,
-            fill: ui.visuals().dark_bg_color,
+            fill: ui.visuals().extreme_bg_color,
             stroke: ui.style().noninteractive().bg_stroke,
         }];
 
         let rect = rect.shrink(4.0);
-        let line_stroke = Stroke::new(1.0, Color32::from_additive_luminance(128));
+        let color = ui.visuals().text_color();
+        let line_stroke = Stroke::new(1.0, color);
 
         if let Some(pointer_pos) = ui.input().pointer.tooltip_pos() {
             if rect.contains(pointer_pos) {
@@ -94,12 +95,12 @@ impl FrameHistory {
                     egui::Align2::LEFT_BOTTOM,
                     text,
                     TextStyle::Monospace,
-                    Color32::WHITE,
+                    color,
                 ));
             }
         }
 
-        let circle_color = Color32::from_additive_luminance(196);
+        let circle_color = color;
         let radius = 2.0;
         let right_side_time = ui.input().time; // Time at right side of screen
 
diff --git a/egui_demo_lib/src/wrap_app.rs b/egui_demo_lib/src/wrap_app.rs
index 6569d7d6..2bd5aa65 100644
--- a/egui_demo_lib/src/wrap_app.rs
+++ b/egui_demo_lib/src/wrap_app.rs
@@ -69,6 +69,8 @@ impl epi::App for WrapApp {
             // A menu-bar is a horizontal layout with some special styles applied.
             // egui::menu::bar(ui, |ui| {
             ui.horizontal_wrapped(|ui| {
+                dark_light_mode_switch(ui);
+
                 ui.checkbox(&mut self.backend_panel.open, "💻 Backend");
                 ui.separator();
 
@@ -130,6 +132,15 @@ fn clock_button(ui: &mut egui::Ui, seconds_since_midnight: f64) -> egui::Respons
     ui.add(egui::Button::new(time).text_style(egui::TextStyle::Monospace))
 }
 
+/// Show a button to switch to/from dark/light mode (globally).
+fn dark_light_mode_switch(ui: &mut egui::Ui) {
+    let style: egui::Style = (*ui.ctx().style()).clone();
+    let new_visuals = style.visuals.light_dark_small_toggle_button(ui);
+    if let Some(visuals) = new_visuals {
+        ui.ctx().set_style(egui::Style { visuals, ..style });
+    }
+}
+
 // ----------------------------------------------------------------------------
 
 /// How often we repaint the demo app by default
diff --git a/epaint/src/shadow.rs b/epaint/src/shadow.rs
index 4b89a6e5..d281416c 100644
--- a/epaint/src/shadow.rs
+++ b/epaint/src/shadow.rs
@@ -22,14 +22,22 @@ impl Shadow {
         }
     }
 
-    /// Windows
-    pub fn big() -> Self {
+    /// Subtle and nice on dark backgrounds
+    pub fn big_dark() -> Self {
         Self {
             extrusion: 32.0,
             color: Color32::from_black_alpha(96),
         }
     }
 
+    /// Subtle and nice on white backgrounds
+    pub fn big_light() -> Self {
+        Self {
+            extrusion: 32.0,
+            color: Color32::from_black_alpha(40),
+        }
+    }
+
     pub fn tessellate(&self, rect: emath::Rect, corner_radius: f32) -> Mesh {
         // tessellator.clip_rect = clip_rect; // TODO: culling