diff --git a/CHANGELOG.md b/CHANGELOG.md
index c19304ba37e..e30fc98e40d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,13 +12,15 @@ NOTE: [`epaint`](crates/epaint/CHANGELOG.md), [`eframe`](crates/eframe/CHANGELOG
 * Add `Plot::clamp_grid` to only show grid where there is data ([#2480](https://github.com/emilk/egui/pull/2480)).
 * Add `ScrollArea::drag_to_scroll` if you want to turn off that feature.
 * Add `Response::on_hover_and_drag_cursor`.
-* Add `Window::default_open` ([#2539](https://github.com/emilk/egui/pull/2539))
-* Add `ProgressBar::fill` if you want to set the fill color manually. ([#2618](https://github.com/emilk/egui/pull/2618))
-* Add `Button::rounding` to enable round buttons ([#2539](https://github.com/emilk/egui/pull/2539))
+* Add `Window::default_open` ([#2539](https://github.com/emilk/egui/pull/2539)).
+* Add `ProgressBar::fill` if you want to set the fill color manually. ([#2618](https://github.com/emilk/egui/pull/2618)).
+* Add `Button::rounding` to enable round buttons ([#2616](https://github.com/emilk/egui/pull/2616)).
+* Add `WidgetVisuals::optional_bg_color` - set it to `Color32::TRANSPARENT` to hide button backgrounds ([#2621](https://github.com/emilk/egui/pull/2621)).
 
 ### Changed 🔧
 * Improved plot grid appearance ([#2412](https://github.com/emilk/egui/pull/2412)).
 * Improved the algorithm for picking the number of decimals to show when hovering values in the `Plot`.
+* Default `ComboBox` is now controlled with `Spacing::combo_width` ([#2621](https://github.com/emilk/egui/pull/2621)).
 
 ### Fixed 🐛
 * Expose `TextEdit`'s multiline flag to AccessKit ([#2448](https://github.com/emilk/egui/pull/2448)).
diff --git a/crates/egui/src/containers/collapsing_header.rs b/crates/egui/src/containers/collapsing_header.rs
index 942e06254c4..ea7d52dedeb 100644
--- a/crates/egui/src/containers/collapsing_header.rs
+++ b/crates/egui/src/containers/collapsing_header.rs
@@ -555,7 +555,7 @@ impl CollapsingHeader {
                 ui.painter().add(epaint::RectShape {
                     rect: header_response.rect.expand(visuals.expansion),
                     rounding: visuals.rounding,
-                    fill: visuals.bg_fill,
+                    fill: visuals.weak_bg_fill,
                     stroke: visuals.bg_stroke,
                     // stroke: Default::default(),
                 });
diff --git a/crates/egui/src/containers/combo_box.rs b/crates/egui/src/containers/combo_box.rs
index 9942e899acf..911f9424279 100644
--- a/crates/egui/src/containers/combo_box.rs
+++ b/crates/egui/src/containers/combo_box.rs
@@ -162,9 +162,6 @@ impl ComboBox {
         let button_id = ui.make_persistent_id(id_source);
 
         ui.horizontal(|ui| {
-            if let Some(width) = width {
-                ui.spacing_mut().slider_width = width; // yes, this is ugly. Will remove later.
-            }
             let mut ir = combo_box_dyn(
                 ui,
                 button_id,
@@ -172,6 +169,7 @@ impl ComboBox {
                 menu_contents,
                 icon,
                 wrap_enabled,
+                width,
             );
             if let Some(label) = label {
                 ir.response
@@ -240,6 +238,7 @@ fn combo_box_dyn<'c, R>(
     menu_contents: Box<dyn FnOnce(&mut Ui) -> R + 'c>,
     icon: Option<IconPainter>,
     wrap_enabled: bool,
+    width: Option<f32>,
 ) -> InnerResponse<Option<R>> {
     let popup_id = button_id.with("popup");
 
@@ -263,18 +262,20 @@ fn combo_box_dyn<'c, R>(
 
     let margin = ui.spacing().button_padding;
     let button_response = button_frame(ui, button_id, is_popup_open, Sense::click(), |ui| {
+        let icon_spacing = ui.spacing().icon_spacing;
         // We don't want to change width when user selects something new
         let full_minimum_width = if wrap_enabled {
             // Currently selected value's text will be wrapped if needed, so occupy the available width.
             ui.available_width()
         } else {
-            // Occupy at least the minimum width assigned to Slider and ComboBox.
-            ui.spacing().slider_width - 2.0 * margin.x
+            // Occupy at least the minimum width assigned to ComboBox.
+            let width = width.unwrap_or_else(|| ui.spacing().combo_width);
+            width - 2.0 * margin.x
         };
         let icon_size = Vec2::splat(ui.spacing().icon_width);
         let wrap_width = if wrap_enabled {
             // Use the available width, currently selected value's text will be wrapped if exceeds this value.
-            ui.available_width() - ui.spacing().item_spacing.x - icon_size.x
+            ui.available_width() - icon_spacing - icon_size.x
         } else {
             // Use all the width necessary to display the currently selected value's text.
             f32::INFINITY
@@ -288,7 +289,7 @@ fn combo_box_dyn<'c, R>(
             full_minimum_width
         } else {
             // Occupy at least the minimum width needed to contain the widget with the currently selected value's text.
-            galley.size().x + ui.spacing().item_spacing.x + icon_size.x
+            galley.size().x + icon_spacing + icon_size.x
         };
 
         // Case : wrap_enabled : occupy all the available width.
@@ -390,7 +391,7 @@ fn button_frame(
             epaint::RectShape {
                 rect: outer_rect.expand(visuals.expansion),
                 rounding: visuals.rounding,
-                fill: visuals.bg_fill,
+                fill: visuals.weak_bg_fill,
                 stroke: visuals.bg_stroke,
             },
         );
diff --git a/crates/egui/src/containers/popup.rs b/crates/egui/src/containers/popup.rs
index 4decca3f165..add02b22b51 100644
--- a/crates/egui/src/containers/popup.rs
+++ b/crates/egui/src/containers/popup.rs
@@ -314,6 +314,8 @@ pub fn popup_below_widget<R>(
 ///
 /// Useful for drop-down menus (combo boxes) or suggestion menus under text fields.
 ///
+/// The opened popup will have the same width as the parent.
+///
 /// You must open the popup with [`Memory::open_popup`] or  [`Memory::toggle_popup`].
 ///
 /// Returns `None` if the popup is not open.
diff --git a/crates/egui/src/menu.rs b/crates/egui/src/menu.rs
index 089a290cf3f..46236d6d3f5 100644
--- a/crates/egui/src/menu.rs
+++ b/crates/egui/src/menu.rs
@@ -68,7 +68,7 @@ fn set_menu_style(style: &mut Style) {
     style.spacing.button_padding = vec2(2.0, 0.0);
     style.visuals.widgets.active.bg_stroke = Stroke::NONE;
     style.visuals.widgets.hovered.bg_stroke = Stroke::NONE;
-    style.visuals.widgets.inactive.bg_fill = Color32::TRANSPARENT;
+    style.visuals.widgets.inactive.weak_bg_fill = Color32::TRANSPARENT;
     style.visuals.widgets.inactive.bg_stroke = Stroke::NONE;
 }
 
@@ -180,7 +180,7 @@ fn stationary_menu_impl<'c, R>(
     let mut button = Button::new(title);
 
     if bar_state.open_menu.is_menu_open(menu_id) {
-        button = button.fill(ui.visuals().widgets.open.bg_fill);
+        button = button.fill(ui.visuals().widgets.open.weak_bg_fill);
         button = button.stroke(ui.visuals().widgets.open.bg_stroke);
     }
 
@@ -443,7 +443,7 @@ impl SubMenuButton {
         sub_id: Id,
     ) -> &'a WidgetVisuals {
         if menu_state.is_open(sub_id) {
-            &ui.style().visuals.widgets.hovered
+            &ui.style().visuals.widgets.open
         } else {
             ui.style().interact(response)
         }
@@ -472,7 +472,8 @@ impl SubMenuButton {
             text_galley.size().x + icon_galley.size().x,
             text_galley.size().y.max(icon_galley.size().y),
         );
-        let desired_size = text_and_icon_size + 2.0 * button_padding;
+        let mut desired_size = text_and_icon_size + 2.0 * button_padding;
+        desired_size.y = desired_size.y.at_least(ui.spacing().interact_size.y);
 
         let (rect, response) = ui.allocate_at_least(desired_size, sense);
         response.widget_info(|| {
@@ -492,7 +493,7 @@ impl SubMenuButton {
                 ui.painter().rect_filled(
                     rect.expand(visuals.expansion),
                     visuals.rounding,
-                    visuals.bg_fill,
+                    visuals.weak_bg_fill,
                 );
             }
 
diff --git a/crates/egui/src/style.rs b/crates/egui/src/style.rs
index 963f1b909ae..3078595d5c5 100644
--- a/crates/egui/src/style.rs
+++ b/crates/egui/src/style.rs
@@ -216,6 +216,7 @@ impl Style {
     pub fn interact_selectable(&self, response: &Response, selected: bool) -> WidgetVisuals {
         let mut visuals = *self.visuals.widgets.style(response);
         if selected {
+            visuals.weak_bg_fill = self.visuals.selection.bg_fill;
             visuals.bg_fill = self.visuals.selection.bg_fill;
             // visuals.bg_stroke = self.visuals.selection.stroke;
             visuals.fg_stroke = self.visuals.selection.stroke;
@@ -264,8 +265,11 @@ pub struct Spacing {
     /// Anything clickable should be (at least) this size.
     pub interact_size: Vec2, // TODO(emilk): rename min_interact_size ?
 
-    /// Default width of a [`Slider`] and [`ComboBox`](crate::ComboBox).
-    pub slider_width: f32, // TODO(emilk): rename big_interact_size ?
+    /// Default width of a [`Slider`].
+    pub slider_width: f32,
+
+    /// Default (minimum) width of a [`ComboBox`](crate::ComboBox).
+    pub combo_width: f32,
 
     /// Default width of a [`TextEdit`].
     pub text_edit_width: f32,
@@ -533,7 +537,7 @@ impl Visuals {
     // TODO(emilk): replace with an alpha
     #[inline(always)]
     pub fn fade_out_to_color(&self) -> Color32 {
-        self.widgets.noninteractive.bg_fill
+        self.widgets.noninteractive.weak_bg_fill
     }
 
     /// Returned a "grayed out" version of the given color.
@@ -594,9 +598,17 @@ impl Widgets {
 #[derive(Clone, Copy, Debug, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub struct WidgetVisuals {
-    /// Background color of widget.
+    /// Background color of widgets that must have a background fill,
+    /// such as the slider background, a checkbox background, or a radio button background.
+    ///
+    /// Must never be [`Color32::TRANSPARENT`].
     pub bg_fill: Color32,
 
+    /// Background color of widgets that can _optionally_ have a background fill, such as buttons.
+    ///
+    /// May be [`Color32::TRANSPARENT`].
+    pub weak_bg_fill: Color32,
+
     /// For surrounding rectangle of things that need it,
     /// like buttons, the box of the checkbox, etc.
     /// Should maybe be called `frame_stroke`.
@@ -684,6 +696,7 @@ impl Default for Spacing {
             indent: 18.0, // match checkbox/radio-button with `button_padding.x + icon_width + icon_spacing`
             interact_size: vec2(40.0, 18.0),
             slider_width: 100.0,
+            combo_width: 100.0,
             text_edit_width: 280.0,
             icon_width: 14.0,
             icon_width_inner: 8.0,
@@ -717,8 +730,8 @@ impl Visuals {
             widgets: Widgets::default(),
             selection: Selection::default(),
             hyperlink_color: Color32::from_rgb(90, 170, 255),
-            faint_bg_color: Color32::from_gray(35),
-            extreme_bg_color: Color32::from_gray(10), // e.g. TextEdit background
+            faint_bg_color: Color32::from_additive_luminance(5), // visible, but barely so
+            extreme_bg_color: Color32::from_gray(10),            // e.g. TextEdit background
             code_bg_color: Color32::from_gray(64),
             warn_fg_color: Color32::from_rgb(255, 143, 0), // orange
             error_fg_color: Color32::from_rgb(255, 0, 0),  // red
@@ -751,8 +764,8 @@ impl Visuals {
             widgets: Widgets::light(),
             selection: Selection::light(),
             hyperlink_color: Color32::from_rgb(0, 155, 255),
-            faint_bg_color: Color32::from_gray(242),
-            extreme_bg_color: Color32::from_gray(255), // e.g. TextEdit background
+            faint_bg_color: Color32::from_additive_luminance(5), // visible, but barely so
+            extreme_bg_color: Color32::from_gray(255),           // e.g. TextEdit background
             code_bg_color: Color32::from_gray(230),
             warn_fg_color: Color32::from_rgb(255, 100, 0), // slightly orange red. it's difficult to find a warning color that pops on bright background.
             error_fg_color: Color32::from_rgb(255, 0, 0),  // red
@@ -801,6 +814,7 @@ impl Widgets {
     pub fn dark() -> Self {
         Self {
             noninteractive: WidgetVisuals {
+                weak_bg_fill: Color32::from_gray(27),
                 bg_fill: Color32::from_gray(27),
                 bg_stroke: Stroke::new(1.0, Color32::from_gray(60)), // separators, indentation lines
                 fg_stroke: Stroke::new(1.0, Color32::from_gray(140)), // normal text color
@@ -808,13 +822,15 @@ impl Widgets {
                 expansion: 0.0,
             },
             inactive: WidgetVisuals {
-                bg_fill: Color32::from_gray(60), // button background
+                weak_bg_fill: Color32::from_gray(60), // button background
+                bg_fill: Color32::from_gray(60),      // checkbox background
                 bg_stroke: Default::default(),
                 fg_stroke: Stroke::new(1.0, Color32::from_gray(180)), // button text
                 rounding: Rounding::same(2.0),
                 expansion: 0.0,
             },
             hovered: WidgetVisuals {
+                weak_bg_fill: Color32::from_gray(70),
                 bg_fill: Color32::from_gray(70),
                 bg_stroke: Stroke::new(1.0, Color32::from_gray(150)), // e.g. hover over window edge or button
                 fg_stroke: Stroke::new(1.5, Color32::from_gray(240)),
@@ -822,6 +838,7 @@ impl Widgets {
                 expansion: 1.0,
             },
             active: WidgetVisuals {
+                weak_bg_fill: Color32::from_gray(55),
                 bg_fill: Color32::from_gray(55),
                 bg_stroke: Stroke::new(1.0, Color32::WHITE),
                 fg_stroke: Stroke::new(2.0, Color32::WHITE),
@@ -829,6 +846,7 @@ impl Widgets {
                 expansion: 1.0,
             },
             open: WidgetVisuals {
+                weak_bg_fill: Color32::from_gray(27),
                 bg_fill: Color32::from_gray(27),
                 bg_stroke: Stroke::new(1.0, Color32::from_gray(60)),
                 fg_stroke: Stroke::new(1.0, Color32::from_gray(210)),
@@ -841,6 +859,7 @@ impl Widgets {
     pub fn light() -> Self {
         Self {
             noninteractive: WidgetVisuals {
+                weak_bg_fill: Color32::from_gray(248),
                 bg_fill: Color32::from_gray(248),
                 bg_stroke: Stroke::new(1.0, Color32::from_gray(190)), // separators, indentation lines
                 fg_stroke: Stroke::new(1.0, Color32::from_gray(80)),  // normal text color
@@ -848,13 +867,15 @@ impl Widgets {
                 expansion: 0.0,
             },
             inactive: WidgetVisuals {
-                bg_fill: Color32::from_gray(230), // button background
+                weak_bg_fill: Color32::from_gray(230), // button background
+                bg_fill: Color32::from_gray(230),      // checkbox background
                 bg_stroke: Default::default(),
                 fg_stroke: Stroke::new(1.0, Color32::from_gray(60)), // button text
                 rounding: Rounding::same(2.0),
                 expansion: 0.0,
             },
             hovered: WidgetVisuals {
+                weak_bg_fill: Color32::from_gray(220),
                 bg_fill: Color32::from_gray(220),
                 bg_stroke: Stroke::new(1.0, Color32::from_gray(105)), // e.g. hover over window edge or button
                 fg_stroke: Stroke::new(1.5, Color32::BLACK),
@@ -862,6 +883,7 @@ impl Widgets {
                 expansion: 1.0,
             },
             active: WidgetVisuals {
+                weak_bg_fill: Color32::from_gray(165),
                 bg_fill: Color32::from_gray(165),
                 bg_stroke: Stroke::new(1.0, Color32::BLACK),
                 fg_stroke: Stroke::new(2.0, Color32::BLACK),
@@ -869,6 +891,7 @@ impl Widgets {
                 expansion: 1.0,
             },
             open: WidgetVisuals {
+                weak_bg_fill: Color32::from_gray(220),
                 bg_fill: Color32::from_gray(220),
                 bg_stroke: Stroke::new(1.0, Color32::from_gray(160)),
                 fg_stroke: Stroke::new(1.0, Color32::BLACK),
@@ -984,6 +1007,7 @@ impl Spacing {
             indent,
             interact_size,
             slider_width,
+            combo_width,
             text_edit_width,
             icon_width,
             icon_width_inner,
@@ -1012,6 +1036,10 @@ impl Spacing {
             ui.add(DragValue::new(slider_width).clamp_range(0.0..=1000.0));
             ui.label("Slider width");
         });
+        ui.horizontal(|ui| {
+            ui.add(DragValue::new(combo_width).clamp_range(0.0..=1000.0));
+            ui.label("ComboBox width");
+        });
         ui.horizontal(|ui| {
             ui.add(DragValue::new(text_edit_width).clamp_range(0.0..=1000.0));
             ui.label("TextEdit width");
@@ -1185,13 +1213,17 @@ impl Selection {
 impl WidgetVisuals {
     pub fn ui(&mut self, ui: &mut crate::Ui) {
         let Self {
-            bg_fill,
+            weak_bg_fill,
+            bg_fill: mandatory_bg_fill,
             bg_stroke,
             rounding,
             fg_stroke,
             expansion,
         } = self;
-        ui_color(ui, bg_fill, "background fill");
+        ui_color(ui, weak_bg_fill, "optional background fill")
+            .on_hover_text("For buttons, combo-boxes, etc");
+        ui_color(ui, mandatory_bg_fill, "mandatory background fill")
+            .on_hover_text("For checkboxes, sliders, etc");
         stroke_ui(ui, bg_stroke, "background stroke");
 
         rounding_ui(ui, rounding);
@@ -1270,7 +1302,7 @@ impl Visuals {
         } = self;
 
         ui.collapsing("Background Colors", |ui| {
-            ui_color(ui, &mut widgets.inactive.bg_fill, "Buttons");
+            ui_color(ui, &mut widgets.inactive.weak_bg_fill, "Buttons");
             ui_color(ui, window_fill, "Windows");
             ui_color(ui, panel_fill, "Panels");
             ui_color(ui, faint_bg_color, "Faint accent").on_hover_text(
diff --git a/crates/egui/src/widgets/button.rs b/crates/egui/src/widgets/button.rs
index e485dbb9337..8f4ad6bbe93 100644
--- a/crates/egui/src/widgets/button.rs
+++ b/crates/egui/src/widgets/button.rs
@@ -180,10 +180,10 @@ impl Widget for Button {
             desired_size.x += ui.spacing().item_spacing.x + shortcut_text.size().x;
             desired_size.y = desired_size.y.max(shortcut_text.size().y);
         }
+        desired_size += 2.0 * button_padding;
         if !small {
             desired_size.y = desired_size.y.at_least(ui.spacing().interact_size.y);
         }
-        desired_size += 2.0 * button_padding;
         desired_size = desired_size.at_least(min_size);
 
         let (rect, response) = ui.allocate_at_least(desired_size, sense);
@@ -193,7 +193,7 @@ impl Widget for Button {
             let visuals = ui.style().interact(&response);
 
             if frame {
-                let fill = fill.unwrap_or(visuals.bg_fill);
+                let fill = fill.unwrap_or(visuals.weak_bg_fill);
                 let stroke = stroke.unwrap_or(visuals.bg_stroke);
                 let rounding = rounding.unwrap_or(visuals.rounding);
                 ui.painter()
@@ -540,7 +540,7 @@ impl Widget for ImageButton {
                 (
                     expansion,
                     visuals.rounding,
-                    visuals.bg_fill,
+                    visuals.weak_bg_fill,
                     visuals.bg_stroke,
                 )
             } else {
diff --git a/crates/egui/src/widgets/progress_bar.rs b/crates/egui/src/widgets/progress_bar.rs
index 6762a2dd209..89f4b0bf28e 100644
--- a/crates/egui/src/widgets/progress_bar.rs
+++ b/crates/egui/src/widgets/progress_bar.rs
@@ -127,10 +127,8 @@ impl Widget for ProgressBar {
                             + vec2(-rounding, 0.0)
                     })
                     .collect();
-                ui.painter().add(Shape::line(
-                    points,
-                    Stroke::new(2.0, visuals.faint_bg_color),
-                ));
+                ui.painter()
+                    .add(Shape::line(points, Stroke::new(2.0, visuals.text_color())));
             }
 
             if let Some(text_kind) = text {
diff --git a/crates/egui/src/widgets/selected_label.rs b/crates/egui/src/widgets/selected_label.rs
index 2f2d49d23d7..86024ae3538 100644
--- a/crates/egui/src/widgets/selected_label.rs
+++ b/crates/egui/src/widgets/selected_label.rs
@@ -64,8 +64,12 @@ impl Widget for SelectableLabel {
             if selected || response.hovered() || response.has_focus() {
                 let rect = rect.expand(visuals.expansion);
 
-                ui.painter()
-                    .rect(rect, visuals.rounding, visuals.bg_fill, visuals.bg_stroke);
+                ui.painter().rect(
+                    rect,
+                    visuals.rounding,
+                    visuals.weak_bg_fill,
+                    visuals.bg_stroke,
+                );
             }
 
             text.paint_with_visuals(ui.painter(), text_pos, &visuals);
diff --git a/crates/egui/src/widgets/slider.rs b/crates/egui/src/widgets/slider.rs
index 0142e2e3f63..9d03fa06d20 100644
--- a/crates/egui/src/widgets/slider.rs
+++ b/crates/egui/src/widgets/slider.rs
@@ -624,11 +624,7 @@ impl<'a> Slider<'a> {
                 rect: rail_rect,
                 rounding: ui.visuals().widgets.inactive.rounding,
                 fill: ui.visuals().widgets.inactive.bg_fill,
-                // fill: visuals.bg_fill,
-                // fill: ui.visuals().extreme_bg_color,
                 stroke: Default::default(),
-                // stroke: visuals.bg_stroke,
-                // stroke: ui.visuals().widgets.inactive.bg_stroke,
             });
 
             let center = self.marker_center(position_1d, &rail_rect);
diff --git a/crates/egui_demo_lib/src/demo/widget_gallery.rs b/crates/egui_demo_lib/src/demo/widget_gallery.rs
index 22d4ac06d37..d91ae395e74 100644
--- a/crates/egui_demo_lib/src/demo/widget_gallery.rs
+++ b/crates/egui_demo_lib/src/demo/widget_gallery.rs
@@ -175,6 +175,8 @@ impl WidgetGallery {
         egui::ComboBox::from_label("Take your pick")
             .selected_text(format!("{:?}", radio))
             .show_ui(ui, |ui| {
+                ui.style_mut().wrap = Some(false);
+                ui.set_min_width(60.0);
                 ui.selectable_value(radio, Enum::First, "First");
                 ui.selectable_value(radio, Enum::Second, "Second");
                 ui.selectable_value(radio, Enum::Third, "Third");
diff --git a/crates/egui_extras/src/datepicker/button.rs b/crates/egui_extras/src/datepicker/button.rs
index 9c5cb11188f..2a07ba9c784 100644
--- a/crates/egui_extras/src/datepicker/button.rs
+++ b/crates/egui_extras/src/datepicker/button.rs
@@ -76,7 +76,7 @@ impl<'a> Widget for DatePickerButton<'a> {
         }
         let mut button = Button::new(text);
         if button_state.picker_visible {
-            button = button.fill(visuals.bg_fill).stroke(visuals.bg_stroke);
+            button = button.fill(visuals.weak_bg_fill).stroke(visuals.bg_stroke);
         }
         let mut button_response = ui.add(button);
         if button_response.clicked() {