Introduce `Custom` variants for every style in the built-in `Theme`

34 files changed, 576 insertions, 286 deletions

diff --git a/examples/solar_system/src/main.rs b/examples/solar_system/src/main.rs
index 56787a99..9e303576 100644
--- a/examples/solar_system/src/main.rs
+++ b/examples/solar_system/src/main.rs
@@ -79,10 +79,14 @@ impl Application for SolarSystem {
     }
 
     fn style(&self) -> theme::Application {
-        theme::Application::Custom(|_theme| application::Appearance {
-            background_color: Color::BLACK,
-            text_color: Color::WHITE,
-        })
+        fn dark_background(_theme: &Theme) -> application::Appearance {
+            application::Appearance {
+                background_color: Color::BLACK,
+                text_color: Color::WHITE,
+            }
+        }
+
+        theme::Application::from(dark_background as fn(&Theme) -> _)
     }
 
     fn subscription(&self) -> Subscription<Message> {
diff --git a/native/src/overlay/menu.rs b/native/src/overlay/menu.rs
index 08135872..3b55eba1 100644
--- a/native/src/overlay/menu.rs
+++ b/native/src/overlay/menu.rs
@@ -178,7 +178,7 @@ where
             font,
             text_size,
             padding,
-            style,
+            style: style.clone(),
         }));
 
         state.tree.diff(&container as &dyn Widget<_, _>);
@@ -288,7 +288,7 @@ where
         layout: Layout<'_>,
         cursor_position: Point,
     ) {
-        let appearance = theme.appearance(self.style);
+        let appearance = theme.appearance(&self.style);
         let bounds = layout.bounds();
 
         renderer.fill_quad(
@@ -460,7 +460,7 @@ where
         _cursor_position: Point,
         viewport: &Rectangle,
     ) {
-        let appearance = theme.appearance(self.style);
+        let appearance = theme.appearance(&self.style);
         let bounds = layout.bounds();
 
         let text_size =
diff --git a/native/src/widget/button.rs b/native/src/widget/button.rs
index 1582188b..fa5da24b 100644
--- a/native/src/widget/button.rs
+++ b/native/src/widget/button.rs
@@ -231,7 +231,7 @@ where
             cursor_position,
             self.on_press.is_some(),
             theme,
-            self.style,
+            &self.style,
             || tree.state.downcast_ref::<State>(),
         );
 
@@ -361,7 +361,7 @@ pub fn draw<'a, Renderer: crate::Renderer>(
     style_sheet: &dyn StyleSheet<
         Style = <Renderer::Theme as StyleSheet>::Style,
     >,
-    style: <Renderer::Theme as StyleSheet>::Style,
+    style: &<Renderer::Theme as StyleSheet>::Style,
     state: impl FnOnce() -> &'a State,
 ) -> Appearance
 where
diff --git a/native/src/widget/checkbox.rs b/native/src/widget/checkbox.rs
index dc3c0bd0..77d639a9 100644
--- a/native/src/widget/checkbox.rs
+++ b/native/src/widget/checkbox.rs
@@ -224,9 +224,9 @@ where
         let mut children = layout.children();
 
         let custom_style = if is_mouse_over {
-            theme.hovered(self.style, self.is_checked)
+            theme.hovered(&self.style, self.is_checked)
         } else {
-            theme.active(self.style, self.is_checked)
+            theme.active(&self.style, self.is_checked)
         };
 
         {
diff --git a/native/src/widget/container.rs b/native/src/widget/container.rs
index 10a80b58..16537c50 100644
--- a/native/src/widget/container.rs
+++ b/native/src/widget/container.rs
@@ -228,7 +228,7 @@ where
         cursor_position: Point,
         viewport: &Rectangle,
     ) {
-        let style = theme.appearance(self.style);
+        let style = theme.appearance(&self.style);
 
         draw_background(renderer, &style, layout.bounds());
 
diff --git a/native/src/widget/helpers.rs b/native/src/widget/helpers.rs
index 79751878..fe6fb815 100644
--- a/native/src/widget/helpers.rs
+++ b/native/src/widget/helpers.rs
@@ -1,4 +1,5 @@
 //! Helper functions to create pure widgets.
+use crate::overlay;
 use crate::widget;
 use crate::{Element, Length};
 
@@ -84,6 +85,7 @@ pub fn button<'a, Message, Renderer>(
 where
     Renderer: crate::Renderer,
     Renderer::Theme: widget::button::StyleSheet,
+    <Renderer::Theme as widget::button::StyleSheet>::Style: Default,
 {
     widget::Button::new(content)
 }
@@ -208,7 +210,12 @@ where
     T: ToString + Eq + 'static,
     [T]: ToOwned<Owned = Vec<T>>,
     Renderer: crate::text::Renderer,
-    Renderer::Theme: widget::pick_list::StyleSheet,
+    Renderer::Theme: widget::pick_list::StyleSheet
+        + widget::scrollable::StyleSheet
+        + overlay::menu::StyleSheet
+        + widget::container::StyleSheet,
+    <Renderer::Theme as overlay::menu::StyleSheet>::Style:
+        From<<Renderer::Theme as widget::pick_list::StyleSheet>::Style>,
 {
     widget::PickList::new(options, selected, on_selected)
 }
diff --git a/native/src/widget/pane_grid.rs b/native/src/widget/pane_grid.rs
index fd771f8b..ff902aa7 100644
--- a/native/src/widget/pane_grid.rs
+++ b/native/src/widget/pane_grid.rs
@@ -401,7 +401,7 @@ where
             viewport,
             self.spacing,
             self.on_resize.as_ref().map(|(leeway, _)| *leeway),
-            self.style,
+            &self.style,
             self.contents
                 .iter()
                 .zip(&tree.children)
@@ -727,7 +727,7 @@ pub fn draw<Renderer, T>(
     viewport: &Rectangle,
     spacing: u16,
     resize_leeway: Option<u16>,
-    style: <Renderer::Theme as StyleSheet>::Style,
+    style: &<Renderer::Theme as StyleSheet>::Style,
     contents: impl Iterator<Item = (Pane, T)>,
     draw_pane: impl Fn(
         T,
diff --git a/native/src/widget/pane_grid/content.rs b/native/src/widget/pane_grid/content.rs
index c236d820..405dc0b2 100644
--- a/native/src/widget/pane_grid/content.rs
+++ b/native/src/widget/pane_grid/content.rs
@@ -103,7 +103,7 @@ where
         let bounds = layout.bounds();
 
         {
-            let style = theme.appearance(self.style);
+            let style = theme.appearance(&self.style);
 
             container::draw_background(renderer, &style, bounds);
         }
diff --git a/native/src/widget/pane_grid/title_bar.rs b/native/src/widget/pane_grid/title_bar.rs
index eb85f924..783a14c3 100644
--- a/native/src/widget/pane_grid/title_bar.rs
+++ b/native/src/widget/pane_grid/title_bar.rs
@@ -129,7 +129,7 @@ where
         use container::StyleSheet;
 
         let bounds = layout.bounds();
-        let style = theme.appearance(self.style);
+        let style = theme.appearance(&self.style);
         let inherited_style = renderer::Style {
             text_color: style.text_color.unwrap_or(inherited_style.text_color),
         };
diff --git a/native/src/widget/pick_list.rs b/native/src/widget/pick_list.rs
index 896f5b35..a6459cd6 100644
--- a/native/src/widget/pick_list.rs
+++ b/native/src/widget/pick_list.rs
@@ -9,6 +9,8 @@ use crate::overlay::menu::{self, Menu};
 use crate::renderer;
 use crate::text::{self, Text};
 use crate::touch;
+use crate::widget::container;
+use crate::widget::scrollable;
 use crate::widget::tree::{self, Tree};
 use crate::{
     Clipboard, Element, Layout, Length, Padding, Point, Rectangle, Shell, Size,
@@ -42,7 +44,12 @@ where
     T: ToString + Eq,
     [T]: ToOwned<Owned = Vec<T>>,
     Renderer: text::Renderer,
-    Renderer::Theme: StyleSheet,
+    Renderer::Theme: StyleSheet
+        + scrollable::StyleSheet
+        + menu::StyleSheet
+        + container::StyleSheet,
+    <Renderer::Theme as menu::StyleSheet>::Style:
+        From<<Renderer::Theme as StyleSheet>::Style>,
 {
     /// The default padding of a [`PickList`].
     pub const DEFAULT_PADDING: Padding = Padding::new(5);
@@ -114,7 +121,12 @@ where
     [T]: ToOwned<Owned = Vec<T>>,
     Message: 'a,
     Renderer: text::Renderer + 'a,
-    Renderer::Theme: StyleSheet,
+    Renderer::Theme: StyleSheet
+        + scrollable::StyleSheet
+        + menu::StyleSheet
+        + container::StyleSheet,
+    <Renderer::Theme as menu::StyleSheet>::Style:
+        From<<Renderer::Theme as StyleSheet>::Style>,
 {
     fn tag(&self) -> tree::Tag {
         tree::Tag::of::<State<T>>()
@@ -202,7 +214,7 @@ where
             &self.font,
             self.placeholder.as_deref(),
             self.selected.as_ref(),
-            self.style,
+            &self.style,
         )
     }
 
@@ -221,7 +233,7 @@ where
             self.text_size,
             self.font.clone(),
             &self.options,
-            self.style,
+            self.style.clone(),
         )
     }
 }
@@ -233,7 +245,12 @@ where
     [T]: ToOwned<Owned = Vec<T>>,
     Message: 'a,
     Renderer: text::Renderer + 'a,
-    Renderer::Theme: StyleSheet,
+    Renderer::Theme: StyleSheet
+        + scrollable::StyleSheet
+        + menu::StyleSheet
+        + container::StyleSheet,
+    <Renderer::Theme as menu::StyleSheet>::Style:
+        From<<Renderer::Theme as StyleSheet>::Style>,
 {
     fn from(pick_list: PickList<'a, T, Message, Renderer>) -> Self {
         Self::new(pick_list)
@@ -456,7 +473,12 @@ where
     T: Clone + ToString,
     Message: 'a,
     Renderer: text::Renderer + 'a,
-    Renderer::Theme: StyleSheet,
+    Renderer::Theme: StyleSheet
+        + scrollable::StyleSheet
+        + menu::StyleSheet
+        + container::StyleSheet,
+    <Renderer::Theme as menu::StyleSheet>::Style:
+        From<<Renderer::Theme as StyleSheet>::Style>,
 {
     if state.is_open {
         let bounds = layout.bounds();
@@ -493,7 +515,7 @@ pub fn draw<T, Renderer>(
     font: &Renderer::Font,
     placeholder: Option<&str>,
     selected: Option<&T>,
-    style: <Renderer::Theme as StyleSheet>::Style,
+    style: &<Renderer::Theme as StyleSheet>::Style,
 ) where
     Renderer: text::Renderer,
     Renderer::Theme: StyleSheet,
diff --git a/native/src/widget/progress_bar.rs b/native/src/widget/progress_bar.rs
index 8a945433..b053d959 100644
--- a/native/src/widget/progress_bar.rs
+++ b/native/src/widget/progress_bar.rs
@@ -124,7 +124,7 @@ where
                 / (range_end - range_start)
         };
 
-        let style = theme.appearance(self.style);
+        let style = theme.appearance(&self.style);
 
         renderer.fill_quad(
             renderer::Quad {
diff --git a/native/src/widget/radio.rs b/native/src/widget/radio.rs
index cb83f745..743689c7 100644
--- a/native/src/widget/radio.rs
+++ b/native/src/widget/radio.rs
@@ -230,9 +230,9 @@ where
         let mut children = layout.children();
 
         let custom_style = if is_mouse_over {
-            theme.hovered(self.style, self.is_selected)
+            theme.hovered(&self.style, self.is_selected)
         } else {
-            theme.active(self.style, self.is_selected)
+            theme.active(&self.style, self.is_selected)
         };
 
         {
diff --git a/native/src/widget/rule.rs b/native/src/widget/rule.rs
index 56f8c80d..e44d8d99 100644
--- a/native/src/widget/rule.rs
+++ b/native/src/widget/rule.rs
@@ -88,7 +88,7 @@ where
         _viewport: &Rectangle,
     ) {
         let bounds = layout.bounds();
-        let style = theme.style(self.style);
+        let style = theme.appearance(&self.style);
 
         let bounds = if self.is_horizontal {
             let line_y = (bounds.y + (bounds.height / 2.0)
diff --git a/native/src/widget/scrollable.rs b/native/src/widget/scrollable.rs
index 4ebb07a0..b257cbe5 100644
--- a/native/src/widget/scrollable.rs
+++ b/native/src/widget/scrollable.rs
@@ -233,7 +233,7 @@ where
             self.scrollbar_width,
             self.scrollbar_margin,
             self.scroller_width,
-            self.style,
+            &self.style,
             |renderer, layout, cursor_position, viewport| {
                 self.content.as_widget().draw(
                     &tree.children[0],
@@ -627,7 +627,7 @@ pub fn draw<Renderer>(
     scrollbar_width: u16,
     scrollbar_margin: u16,
     scroller_width: u16,
-    style: <Renderer::Theme as StyleSheet>::Style,
+    style: &<Renderer::Theme as StyleSheet>::Style,
     draw_content: impl FnOnce(&mut Renderer, Layout<'_>, Point, &Rectangle),
 ) where
     Renderer: crate::Renderer,
diff --git a/native/src/widget/slider.rs b/native/src/widget/slider.rs
index 585d9c35..92ed72e9 100644
--- a/native/src/widget/slider.rs
+++ b/native/src/widget/slider.rs
@@ -222,7 +222,7 @@ where
             self.value,
             &self.range,
             theme,
-            self.style,
+            &self.style,
         )
     }
 
@@ -353,7 +353,7 @@ pub fn draw<T, R>(
     value: T,
     range: &RangeInclusive<T>,
     style_sheet: &dyn StyleSheet<Style = <R::Theme as StyleSheet>::Style>,
-    style: <R::Theme as StyleSheet>::Style,
+    style: &<R::Theme as StyleSheet>::Style,
 ) where
     T: Into<f64> + Copy,
     R: crate::Renderer,
@@ -363,11 +363,11 @@ pub fn draw<T, R>(
     let is_mouse_over = bounds.contains(cursor_position);
 
     let style = if state.is_dragging {
-        style_sheet.dragging(style)
+        style_sheet.dragging(&style)
     } else if is_mouse_over {
-        style_sheet.hovered(style)
+        style_sheet.hovered(&style)
     } else {
-        style_sheet.active(style)
+        style_sheet.active(&style)
     };
 
     let rail_y = bounds.y + (bounds.height / 2.0).round();
diff --git a/native/src/widget/text_input.rs b/native/src/widget/text_input.rs
index 25a8690e..22eff7f1 100644
--- a/native/src/widget/text_input.rs
+++ b/native/src/widget/text_input.rs
@@ -188,7 +188,7 @@ where
             self.size,
             &self.font,
             self.is_secure,
-            self.style,
+            &self.style,
         )
     }
 }
@@ -284,7 +284,7 @@ where
             self.size,
             &self.font,
             self.is_secure,
-            self.style,
+            &self.style,
         )
     }
 
@@ -746,7 +746,7 @@ pub fn draw<Renderer>(
     size: Option<u16>,
     font: &Renderer::Font,
     is_secure: bool,
-    style: <Renderer::Theme as StyleSheet>::Style,
+    style: &<Renderer::Theme as StyleSheet>::Style,
 ) where
     Renderer: text::Renderer,
     Renderer::Theme: StyleSheet,
diff --git a/native/src/widget/toggler.rs b/native/src/widget/toggler.rs
index 7893f78c..99a56ea8 100644
--- a/native/src/widget/toggler.rs
+++ b/native/src/widget/toggler.rs
@@ -260,9 +260,9 @@ where
         let is_mouse_over = bounds.contains(cursor_position);
 
         let style = if is_mouse_over {
-            theme.hovered(self.style, self.is_active)
+            theme.hovered(&self.style, self.is_active)
         } else {
-            theme.active(self.style, self.is_active)
+            theme.active(&self.style, self.is_active)
         };
 
         let border_radius = bounds.height as f32 / BORDER_RADIUS_RATIO;
diff --git a/native/src/widget/tooltip.rs b/native/src/widget/tooltip.rs
index 674f2ba6..9347a886 100644
--- a/native/src/widget/tooltip.rs
+++ b/native/src/widget/tooltip.rs
@@ -201,7 +201,7 @@ where
             self.gap,
             self.padding,
             self.snap_within_viewport,
-            self.style,
+            &self.style,
             |renderer, limits| {
                 Widget::<(), Renderer>::layout(tooltip, renderer, limits)
             },
@@ -275,7 +275,7 @@ pub fn draw<Renderer>(
     gap: u16,
     padding: u16,
     snap_within_viewport: bool,
-    style: <Renderer::Theme as container::StyleSheet>::Style,
+    style: &<Renderer::Theme as container::StyleSheet>::Style,
     layout_text: impl FnOnce(&Renderer, &layout::Limits) -> layout::Node,
     draw_text: impl FnOnce(
         &mut Renderer,
diff --git a/style/src/application.rs b/style/src/application.rs
index d48c6a34..a7f8d11f 100644
--- a/style/src/application.rs
+++ b/style/src/application.rs
@@ -1,9 +1,9 @@
 use iced_core::Color;
 
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
-    fn appearance(&self, style: Self::Style) -> Appearance;
+    fn appearance(&self, style: &Self::Style) -> Appearance;
 }
 
 #[derive(Debug, Clone, Copy, PartialEq)]
diff --git a/style/src/button.rs b/style/src/button.rs
index c63a6b71..858a9ab2 100644
--- a/style/src/button.rs
+++ b/style/src/button.rs
@@ -27,11 +27,11 @@ impl std::default::Default for Appearance {
 
 /// A set of rules that dictate the style of a button.
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
-    fn active(&self, style: Self::Style) -> Appearance;
+    fn active(&self, style: &Self::Style) -> Appearance;
 
-    fn hovered(&self, style: Self::Style) -> Appearance {
+    fn hovered(&self, style: &Self::Style) -> Appearance {
         let active = self.active(style);
 
         Appearance {
@@ -40,14 +40,14 @@ pub trait StyleSheet {
         }
     }
 
-    fn pressed(&self, style: Self::Style) -> Appearance {
+    fn pressed(&self, style: &Self::Style) -> Appearance {
         Appearance {
             shadow_offset: Vector::default(),
             ..self.active(style)
         }
     }
 
-    fn disabled(&self, style: Self::Style) -> Appearance {
+    fn disabled(&self, style: &Self::Style) -> Appearance {
         let active = self.active(style);
 
         Appearance {
diff --git a/style/src/checkbox.rs b/style/src/checkbox.rs
index ba54b0a2..a8b4a11d 100644
--- a/style/src/checkbox.rs
+++ b/style/src/checkbox.rs
@@ -14,9 +14,9 @@ pub struct Appearance {
 
 /// A set of rules that dictate the style of a checkbox.
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
-    fn active(&self, style: Self::Style, is_checked: bool) -> Appearance;
+    fn active(&self, style: &Self::Style, is_checked: bool) -> Appearance;
 
-    fn hovered(&self, style: Self::Style, is_checked: bool) -> Appearance;
+    fn hovered(&self, style: &Self::Style, is_checked: bool) -> Appearance;
 }
diff --git a/style/src/container.rs b/style/src/container.rs
index 184310fa..53c59589 100644
--- a/style/src/container.rs
+++ b/style/src/container.rs
@@ -25,8 +25,8 @@ impl std::default::Default for Appearance {
 
 /// A set of rules that dictate the [`Appearance`] of a container.
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
     /// Produces the [`Appearance`] of a container.
-    fn appearance(&self, style: Self::Style) -> Appearance;
+    fn appearance(&self, style: &Self::Style) -> Appearance;
 }
diff --git a/style/src/menu.rs b/style/src/menu.rs
index 6ef3e2a2..409831a9 100644
--- a/style/src/menu.rs
+++ b/style/src/menu.rs
@@ -13,7 +13,7 @@ pub struct Appearance {
 }
 
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default + Clone;
 
-    fn appearance(&self, style: Self::Style) -> Appearance;
+    fn appearance(&self, style: &Self::Style) -> Appearance;
 }
diff --git a/style/src/pane_grid.rs b/style/src/pane_grid.rs
index 5bae353f..be541434 100644
--- a/style/src/pane_grid.rs
+++ b/style/src/pane_grid.rs
@@ -4,13 +4,13 @@ use iced_core::Color;
 
 /// A set of rules that dictate the style of a container.
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
     /// The [`Line`] to draw when a split is picked.
-    fn picked_split(&self, style: Self::Style) -> Option<Line>;
+    fn picked_split(&self, style: &Self::Style) -> Option<Line>;
 
     /// The [`Line`] to draw when a split is hovered.
-    fn hovered_split(&self, style: Self::Style) -> Option<Line>;
+    fn hovered_split(&self, style: &Self::Style) -> Option<Line>;
 }
 
 /// A line.
diff --git a/style/src/pick_list.rs b/style/src/pick_list.rs
index 2bafe932..a09772d7 100644
--- a/style/src/pick_list.rs
+++ b/style/src/pick_list.rs
@@ -1,9 +1,5 @@
 use iced_core::{Background, Color};
 
-use crate::container;
-use crate::menu;
-use crate::scrollable;
-
 /// The appearance of a pick list.
 #[derive(Debug, Clone, Copy)]
 pub struct Appearance {
@@ -17,13 +13,10 @@ pub struct Appearance {
 }
 
 /// A set of rules that dictate the style of a container.
-pub trait StyleSheet:
-    container::StyleSheet + menu::StyleSheet + scrollable::StyleSheet
-{
-    type Style: Default + Copy + Into<<Self as menu::StyleSheet>::Style>;
+pub trait StyleSheet {
+    type Style: Default + Clone;
 
-    fn active(&self, style: <Self as StyleSheet>::Style) -> Appearance;
+    fn active(&self, style: &<Self as StyleSheet>::Style) -> Appearance;
 
-    /// Produces the style of a container.
-    fn hovered(&self, style: <Self as StyleSheet>::Style) -> Appearance;
+    fn hovered(&self, style: &<Self as StyleSheet>::Style) -> Appearance;
 }
diff --git a/style/src/progress_bar.rs b/style/src/progress_bar.rs
index 768e7c9c..506d634f 100644
--- a/style/src/progress_bar.rs
+++ b/style/src/progress_bar.rs
@@ -11,7 +11,7 @@ pub struct Appearance {
 
 /// A set of rules that dictate the style of a progress bar.
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
-    fn appearance(&self, style: Self::Style) -> Appearance;
+    fn appearance(&self, style: &Self::Style) -> Appearance;
 }
diff --git a/style/src/radio.rs b/style/src/radio.rs
index d14ea33e..370d483e 100644
--- a/style/src/radio.rs
+++ b/style/src/radio.rs
@@ -13,9 +13,9 @@ pub struct Appearance {
 
 /// A set of rules that dictate the style of a radio button.
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
-    fn active(&self, style: Self::Style, is_selected: bool) -> Appearance;
+    fn active(&self, style: &Self::Style, is_selected: bool) -> Appearance;
 
-    fn hovered(&self, style: Self::Style, is_selected: bool) -> Appearance;
+    fn hovered(&self, style: &Self::Style, is_selected: bool) -> Appearance;
 }
diff --git a/style/src/rule.rs b/style/src/rule.rs
index af334912..bcad655c 100644
--- a/style/src/rule.rs
+++ b/style/src/rule.rs
@@ -16,10 +16,10 @@ pub struct Appearance {
 
 /// A set of rules that dictate the style of a rule.
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
     /// Produces the style of a rule.
-    fn style(&self, style: Self::Style) -> Appearance;
+    fn appearance(&self, style: &Self::Style) -> Appearance;
 }
 
 /// The fill mode of a rule.
diff --git a/style/src/scrollable.rs b/style/src/scrollable.rs
index 8da7409c..4352930c 100644
--- a/style/src/scrollable.rs
+++ b/style/src/scrollable.rs
@@ -22,16 +22,16 @@ pub struct Scroller {
 
 /// A set of rules that dictate the style of a scrollable.
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
     /// Produces the style of an active scrollbar.
-    fn active(&self, style: Self::Style) -> Scrollbar;
+    fn active(&self, style: &Self::Style) -> Scrollbar;
 
     /// Produces the style of an hovered scrollbar.
-    fn hovered(&self, style: Self::Style) -> Scrollbar;
+    fn hovered(&self, style: &Self::Style) -> Scrollbar;
 
     /// Produces the style of a scrollbar that is being dragged.
-    fn dragging(&self, style: Self::Style) -> Scrollbar {
+    fn dragging(&self, style: &Self::Style) -> Scrollbar {
         self.hovered(style)
     }
 }
diff --git a/style/src/slider.rs b/style/src/slider.rs
index 0ff0449b..73ee097b 100644
--- a/style/src/slider.rs
+++ b/style/src/slider.rs
@@ -26,14 +26,14 @@ pub enum HandleShape {
 
 /// A set of rules that dictate the style of a slider.
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
     /// Produces the style of an active slider.
-    fn active(&self, style: Self::Style) -> Appearance;
+    fn active(&self, style: &Self::Style) -> Appearance;
 
     /// Produces the style of an hovered slider.
-    fn hovered(&self, style: Self::Style) -> Appearance;
+    fn hovered(&self, style: &Self::Style) -> Appearance;
 
     /// Produces the style of a slider that is being dragged.
-    fn dragging(&self, style: Self::Style) -> Appearance;
+    fn dragging(&self, style: &Self::Style) -> Appearance;
 }
diff --git a/style/src/text_input.rs b/style/src/text_input.rs
index af86617b..1be9ccea 100644
--- a/style/src/text_input.rs
+++ b/style/src/text_input.rs
@@ -12,22 +12,22 @@ pub struct Appearance {
 
 /// A set of rules that dictate the style of a text input.
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
     /// Produces the style of an active text input.
-    fn active(&self, style: Self::Style) -> Appearance;
+    fn active(&self, style: &Self::Style) -> Appearance;
 
     /// Produces the style of a focused text input.
-    fn focused(&self, style: Self::Style) -> Appearance;
+    fn focused(&self, style: &Self::Style) -> Appearance;
 
-    fn placeholder_color(&self, style: Self::Style) -> Color;
+    fn placeholder_color(&self, style: &Self::Style) -> Color;
 
-    fn value_color(&self, style: Self::Style) -> Color;
+    fn value_color(&self, style: &Self::Style) -> Color;
 
-    fn selection_color(&self, style: Self::Style) -> Color;
+    fn selection_color(&self, style: &Self::Style) -> Color;
 
     /// Produces the style of an hovered text input.
-    fn hovered(&self, style: Self::Style) -> Appearance {
+    fn hovered(&self, style: &Self::Style) -> Appearance {
         self.focused(style)
     }
 }
diff --git a/style/src/theme.rs b/style/src/theme.rs
index a253e990..a5a78ab1 100644
--- a/style/src/theme.rs
+++ b/style/src/theme.rs
@@ -19,7 +19,9 @@ use crate::text;
 use crate::text_input;
 use crate::toggler;
 
-use iced_core::{Background, Color};
+use iced_core::{Background, Color, Vector};
+
+use std::rc::Rc;
 
 #[derive(Debug, Clone, PartialEq)]
 pub enum Theme {
@@ -71,10 +73,9 @@ impl Custom {
     }
 }
 
-#[derive(Debug, Clone, Copy)]
 pub enum Application {
     Default,
-    Custom(fn(Theme) -> application::Appearance),
+    Custom(Box<dyn application::StyleSheet<Style = Theme>>),
 }
 
 impl Default for Application {
@@ -86,7 +87,7 @@ impl Default for Application {
 impl application::StyleSheet for Theme {
     type Style = Application;
 
-    fn appearance(&self, style: Self::Style) -> application::Appearance {
+    fn appearance(&self, style: &Self::Style) -> application::Appearance {
         let palette = self.extended_palette();
 
         match style {
@@ -94,21 +95,35 @@ impl application::StyleSheet for Theme {
                 background_color: palette.background.base.color,
                 text_color: palette.background.base.text,
             },
-            Application::Custom(f) => f(self.clone()),
+            Application::Custom(custom) => custom.appearance(self),
         }
     }
 }
 
+impl application::StyleSheet for fn(&Theme) -> application::Appearance {
+    type Style = Theme;
+
+    fn appearance(&self, style: &Self::Style) -> application::Appearance {
+        (self)(style)
+    }
+}
+
+impl From<fn(&Theme) -> application::Appearance> for Application {
+    fn from(f: fn(&Theme) -> application::Appearance) -> Self {
+        Self::Custom(Box::new(f))
+    }
+}
+
 /*
  * Button
  */
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Button {
     Primary,
     Secondary,
     Positive,
     Destructive,
     Text,
+    Custom(Box<dyn button::StyleSheet<Style = Theme>>),
 }
 
 impl Default for Button {
@@ -120,7 +135,7 @@ impl Default for Button {
 impl button::StyleSheet for Theme {
     type Style = Button;
 
-    fn active(&self, style: Self::Style) -> button::Appearance {
+    fn active(&self, style: &Self::Style) -> button::Appearance {
         let palette = self.extended_palette();
 
         let appearance = button::Appearance {
@@ -143,19 +158,25 @@ impl button::StyleSheet for Theme {
                 text_color: palette.background.base.text,
                 ..appearance
             },
+            Button::Custom(custom) => custom.active(self),
         }
     }
 
-    fn hovered(&self, style: Self::Style) -> button::Appearance {
-        let active = self.active(style);
+    fn hovered(&self, style: &Self::Style) -> button::Appearance {
         let palette = self.extended_palette();
 
+        if let Button::Custom(custom) = style {
+            return custom.hovered(self);
+        }
+
+        let active = self.active(style);
+
         let background = match style {
             Button::Primary => Some(palette.primary.base.color),
             Button::Secondary => Some(palette.background.strong.color),
             Button::Positive => Some(palette.success.strong.color),
             Button::Destructive => Some(palette.danger.strong.color),
-            Button::Text => None,
+            Button::Text | Button::Custom(_) => None,
         };
 
         button::Appearance {
@@ -163,17 +184,51 @@ impl button::StyleSheet for Theme {
             ..active
         }
     }
+
+    fn pressed(&self, style: &Self::Style) -> button::Appearance {
+        if let Button::Custom(custom) = style {
+            return custom.pressed(self);
+        }
+
+        button::Appearance {
+            shadow_offset: Vector::default(),
+            ..self.active(style)
+        }
+    }
+
+    fn disabled(&self, style: &Self::Style) -> button::Appearance {
+        if let Button::Custom(custom) = style {
+            return custom.disabled(self);
+        }
+
+        let active = self.active(style);
+
+        button::Appearance {
+            shadow_offset: Vector::default(),
+            background: active.background.map(|background| match background {
+                Background::Color(color) => Background::Color(Color {
+                    a: color.a * 0.5,
+                    ..color
+                }),
+            }),
+            text_color: Color {
+                a: active.text_color.a * 0.5,
+                ..active.text_color
+            },
+            ..active
+        }
+    }
 }
 
 /*
  * Checkbox
  */
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Checkbox {
     Primary,
     Secondary,
     Success,
     Danger,
+    Custom(Box<dyn checkbox::StyleSheet<Style = Theme>>),
 }
 
 impl Default for Checkbox {
@@ -187,7 +242,7 @@ impl checkbox::StyleSheet for Theme {
 
     fn active(
         &self,
-        style: Self::Style,
+        style: &Self::Style,
         is_checked: bool,
     ) -> checkbox::Appearance {
         let palette = self.extended_palette();
@@ -217,12 +272,13 @@ impl checkbox::StyleSheet for Theme {
                 palette.danger.base,
                 is_checked,
             ),
+            Checkbox::Custom(custom) => custom.active(self, is_checked),
         }
     }
 
     fn hovered(
         &self,
-        style: Self::Style,
+        style: &Self::Style,
         is_checked: bool,
     ) -> checkbox::Appearance {
         let palette = self.extended_palette();
@@ -252,6 +308,7 @@ impl checkbox::StyleSheet for Theme {
                 palette.danger.base,
                 is_checked,
             ),
+            Checkbox::Custom(custom) => custom.hovered(self, is_checked),
         }
     }
 }
@@ -279,11 +336,10 @@ fn checkbox_appearance(
 /*
  * Container
  */
-#[derive(Clone, Copy)]
 pub enum Container {
     Transparent,
     Box,
-    Custom(fn(&Theme) -> container::Appearance),
+    Custom(Box<dyn container::StyleSheet<Style = Theme>>),
 }
 
 impl Default for Container {
@@ -294,14 +350,14 @@ impl Default for Container {
 
 impl From<fn(&Theme) -> container::Appearance> for Container {
     fn from(f: fn(&Theme) -> container::Appearance) -> Self {
-        Self::Custom(f)
+        Self::Custom(Box::new(f))
     }
 }
 
 impl container::StyleSheet for Theme {
     type Style = Container;
 
-    fn appearance(&self, style: Self::Style) -> container::Appearance {
+    fn appearance(&self, style: &Self::Style) -> container::Appearance {
         match style {
             Container::Transparent => Default::default(),
             Container::Box => {
@@ -315,63 +371,96 @@ impl container::StyleSheet for Theme {
                     border_color: Color::TRANSPARENT,
                 }
             }
-            Container::Custom(f) => f(self),
+            Container::Custom(custom) => custom.appearance(self),
         }
     }
 }
 
+impl container::StyleSheet for fn(&Theme) -> container::Appearance {
+    type Style = Theme;
+
+    fn appearance(&self, style: &Self::Style) -> container::Appearance {
+        (self)(style)
+    }
+}
+
 /*
  * Slider
  */
-impl slider::StyleSheet for Theme {
-    type Style = ();
+#[derive(Default)]
+pub enum Slider {
+    #[default]
+    Default,
+    Custom(Box<dyn slider::StyleSheet<Style = Theme>>),
+}
 
-    fn active(&self, _style: Self::Style) -> slider::Appearance {
-        let palette = self.extended_palette();
+impl slider::StyleSheet for Theme {
+    type Style = Slider;
 
-        let handle = slider::Handle {
-            shape: slider::HandleShape::Rectangle {
-                width: 8,
-                border_radius: 4.0,
-            },
-            color: Color::WHITE,
-            border_color: Color::WHITE,
-            border_width: 1.0,
-        };
+    fn active(&self, style: &Self::Style) -> slider::Appearance {
+        match style {
+            Slider::Default => {
+                let palette = self.extended_palette();
 
-        slider::Appearance {
-            rail_colors: (palette.primary.base.color, Color::TRANSPARENT),
-            handle: slider::Handle {
-                color: palette.background.base.color,
-                border_color: palette.primary.base.color,
-                ..handle
-            },
+                let handle = slider::Handle {
+                    shape: slider::HandleShape::Rectangle {
+                        width: 8,
+                        border_radius: 4.0,
+                    },
+                    color: Color::WHITE,
+                    border_color: Color::WHITE,
+                    border_width: 1.0,
+                };
+
+                slider::Appearance {
+                    rail_colors: (
+                        palette.primary.base.color,
+                        Color::TRANSPARENT,
+                    ),
+                    handle: slider::Handle {
+                        color: palette.background.base.color,
+                        border_color: palette.primary.base.color,
+                        ..handle
+                    },
+                }
+            }
+            Slider::Custom(custom) => custom.active(self),
         }
     }
 
-    fn hovered(&self, style: Self::Style) -> slider::Appearance {
-        let active = self.active(style);
-        let palette = self.extended_palette();
+    fn hovered(&self, style: &Self::Style) -> slider::Appearance {
+        match style {
+            Slider::Default => {
+                let active = self.active(style);
+                let palette = self.extended_palette();
 
-        slider::Appearance {
-            handle: slider::Handle {
-                color: palette.primary.weak.color,
-                ..active.handle
-            },
-            ..active
+                slider::Appearance {
+                    handle: slider::Handle {
+                        color: palette.primary.weak.color,
+                        ..active.handle
+                    },
+                    ..active
+                }
+            }
+            Slider::Custom(custom) => custom.hovered(self),
         }
     }
 
-    fn dragging(&self, style: Self::Style) -> slider::Appearance {
-        let active = self.active(style);
-        let palette = self.extended_palette();
+    fn dragging(&self, style: &Self::Style) -> slider::Appearance {
+        match style {
+            Slider::Default => {
+                let active = self.active(style);
+                let palette = self.extended_palette();
 
-        slider::Appearance {
-            handle: slider::Handle {
-                color: palette.primary.base.color,
-                ..active.handle
-            },
-            ..active
+                slider::Appearance {
+                    handle: slider::Handle {
+                        color: palette.primary.base.color,
+                        ..active.handle
+                    },
+                    ..active
+                }
+            }
+            Slider::Custom(custom) => custom.dragging(self),
         }
     }
 }
@@ -379,20 +468,41 @@ impl slider::StyleSheet for Theme {
 /*
  * Menu
  */
+#[derive(Clone, Default)]
+pub enum Menu {
+    #[default]
+    Default,
+    Custom(Rc<dyn menu::StyleSheet<Style = Theme>>),
+}
+
 impl menu::StyleSheet for Theme {
-    type Style = ();
+    type Style = Menu;
 
-    fn appearance(&self, _style: Self::Style) -> menu::Appearance {
-        let palette = self.extended_palette();
+    fn appearance(&self, style: &Self::Style) -> menu::Appearance {
+        match style {
+            Menu::Default => {
+                let palette = self.extended_palette();
 
-        menu::Appearance {
-            text_color: palette.background.weak.text,
-            background: palette.background.weak.color.into(),
-            border_width: 1.0,
-            border_radius: 0.0,
-            border_color: palette.background.strong.color,
-            selected_text_color: palette.primary.strong.text,
-            selected_background: palette.primary.strong.color.into(),
+                menu::Appearance {
+                    text_color: palette.background.weak.text,
+                    background: palette.background.weak.color.into(),
+                    border_width: 1.0,
+                    border_radius: 0.0,
+                    border_color: palette.background.strong.color,
+                    selected_text_color: palette.primary.strong.text,
+                    selected_background: palette.primary.strong.color.into(),
+                }
+            }
+            Menu::Custom(custom) => custom.appearance(self),
+        }
+    }
+}
+
+impl From<PickList> for Menu {
+    fn from(pick_list: PickList) -> Self {
+        match pick_list {
+            PickList::Default => Self::Default,
+            PickList::Custom(_, menu) => Self::Custom(menu),
         }
     }
 }
@@ -400,34 +510,54 @@ impl menu::StyleSheet for Theme {
 /*
  * Pick List
  */
+#[derive(Clone, Default)]
+pub enum PickList {
+    #[default]
+    Default,
+    Custom(
+        Rc<dyn pick_list::StyleSheet<Style = Theme>>,
+        Rc<dyn menu::StyleSheet<Style = Theme>>,
+    ),
+}
+
 impl pick_list::StyleSheet for Theme {
-    type Style = ();
+    type Style = PickList;
 
-    fn active(&self, _style: ()) -> pick_list::Appearance {
-        let palette = self.extended_palette();
+    fn active(&self, style: &Self::Style) -> pick_list::Appearance {
+        match style {
+            PickList::Default => {
+                let palette = self.extended_palette();
 
-        pick_list::Appearance {
-            text_color: palette.background.weak.text,
-            background: palette.background.weak.color.into(),
-            placeholder_color: palette.background.strong.color,
-            border_radius: 2.0,
-            border_width: 1.0,
-            border_color: palette.background.strong.color,
-            icon_size: 0.7,
+                pick_list::Appearance {
+                    text_color: palette.background.weak.text,
+                    background: palette.background.weak.color.into(),
+                    placeholder_color: palette.background.strong.color,
+                    border_radius: 2.0,
+                    border_width: 1.0,
+                    border_color: palette.background.strong.color,
+                    icon_size: 0.7,
+                }
+            }
+            PickList::Custom(custom, _) => custom.active(self),
         }
     }
 
-    fn hovered(&self, _style: ()) -> pick_list::Appearance {
-        let palette = self.extended_palette();
+    fn hovered(&self, style: &Self::Style) -> pick_list::Appearance {
+        match style {
+            PickList::Default => {
+                let palette = self.extended_palette();
 
-        pick_list::Appearance {
-            text_color: palette.background.weak.text,
-            background: palette.background.weak.color.into(),
-            placeholder_color: palette.background.strong.color,
-            border_radius: 2.0,
-            border_width: 1.0,
-            border_color: palette.primary.strong.color,
-            icon_size: 0.7,
+                pick_list::Appearance {
+                    text_color: palette.background.weak.text,
+                    background: palette.background.weak.color.into(),
+                    placeholder_color: palette.background.strong.color,
+                    border_radius: 2.0,
+                    border_width: 1.0,
+                    border_color: palette.primary.strong.color,
+                    icon_size: 0.7,
+                }
+            }
+            PickList::Custom(custom, _) => custom.active(self),
         }
     }
 }
@@ -435,37 +565,54 @@ impl pick_list::StyleSheet for Theme {
 /*
  * Radio
  */
+#[derive(Default)]
+pub enum Radio {
+    #[default]
+    Default,
+    Custom(Box<dyn radio::StyleSheet<Style = Theme>>),
+}
+
 impl radio::StyleSheet for Theme {
-    type Style = ();
+    type Style = Radio;
 
     fn active(
         &self,
-        _style: Self::Style,
-        _is_selected: bool,
+        style: &Self::Style,
+        is_selected: bool,
     ) -> radio::Appearance {
-        let palette = self.extended_palette();
+        match style {
+            Radio::Default => {
+                let palette = self.extended_palette();
 
-        radio::Appearance {
-            background: Color::TRANSPARENT.into(),
-            dot_color: palette.primary.strong.color,
-            border_width: 1.0,
-            border_color: palette.primary.strong.color,
-            text_color: None,
+                radio::Appearance {
+                    background: Color::TRANSPARENT.into(),
+                    dot_color: palette.primary.strong.color,
+                    border_width: 1.0,
+                    border_color: palette.primary.strong.color,
+                    text_color: None,
+                }
+            }
+            Radio::Custom(custom) => custom.active(self, is_selected),
         }
     }
 
     fn hovered(
         &self,
-        style: Self::Style,
+        style: &Self::Style,
         is_selected: bool,
     ) -> radio::Appearance {
-        let active = self.active(style, is_selected);
-        let palette = self.extended_palette();
+        match style {
+            Radio::Default => {
+                let active = self.active(style, is_selected);
+                let palette = self.extended_palette();
 
-        radio::Appearance {
-            dot_color: palette.primary.strong.color,
-            background: palette.primary.weak.color.into(),
-            ..active
+                radio::Appearance {
+                    dot_color: palette.primary.strong.color,
+                    background: palette.primary.weak.color.into(),
+                    ..active
+                }
+            }
+            Radio::Custom(custom) => custom.hovered(self, is_selected),
         }
     }
 }
@@ -473,49 +620,66 @@ impl radio::StyleSheet for Theme {
 /*
  * Toggler
  */
+#[derive(Default)]
+pub enum Toggler {
+    #[default]
+    Default,
+    Custom(Box<dyn toggler::StyleSheet<Style = Theme>>),
+}
+
 impl toggler::StyleSheet for Theme {
-    type Style = ();
+    type Style = Toggler;
 
     fn active(
         &self,
-        _style: Self::Style,
+        style: &Self::Style,
         is_active: bool,
     ) -> toggler::Appearance {
-        let palette = self.extended_palette();
+        match style {
+            Toggler::Default => {
+                let palette = self.extended_palette();
 
-        toggler::Appearance {
-            background: if is_active {
-                palette.primary.strong.color
-            } else {
-                palette.background.strong.color
-            },
-            background_border: None,
-            foreground: if is_active {
-                palette.primary.strong.text
-            } else {
-                palette.background.base.color
-            },
-            foreground_border: None,
+                toggler::Appearance {
+                    background: if is_active {
+                        palette.primary.strong.color
+                    } else {
+                        palette.background.strong.color
+                    },
+                    background_border: None,
+                    foreground: if is_active {
+                        palette.primary.strong.text
+                    } else {
+                        palette.background.base.color
+                    },
+                    foreground_border: None,
+                }
+            }
+            Toggler::Custom(custom) => custom.active(self, is_active),
         }
     }
 
     fn hovered(
         &self,
-        style: Self::Style,
+        style: &Self::Style,
         is_active: bool,
     ) -> toggler::Appearance {
-        let palette = self.extended_palette();
+        match style {
+            Toggler::Default => {
+                let palette = self.extended_palette();
 
-        toggler::Appearance {
-            foreground: if is_active {
-                Color {
-                    a: 0.5,
-                    ..palette.primary.strong.text
+                toggler::Appearance {
+                    foreground: if is_active {
+                        Color {
+                            a: 0.5,
+                            ..palette.primary.strong.text
+                        }
+                    } else {
+                        palette.background.weak.color
+                    },
+                    ..self.active(style, is_active)
                 }
-            } else {
-                palette.background.weak.color
-            },
-            ..self.active(style, is_active)
+            }
+            Toggler::Custom(custom) => custom.hovered(self, is_active),
         }
     }
 }
@@ -523,37 +687,53 @@ impl toggler::StyleSheet for Theme {
 /*
  * Pane Grid
  */
+#[derive(Default)]
+pub enum PaneGrid {
+    #[default]
+    Default,
+    Custom(Box<dyn pane_grid::StyleSheet<Style = Theme>>),
+}
+
 impl pane_grid::StyleSheet for Theme {
-    type Style = ();
+    type Style = PaneGrid;
 
-    fn picked_split(&self, _style: Self::Style) -> Option<pane_grid::Line> {
-        let palette = self.extended_palette();
+    fn picked_split(&self, style: &Self::Style) -> Option<pane_grid::Line> {
+        match style {
+            PaneGrid::Default => {
+                let palette = self.extended_palette();
 
-        Some(pane_grid::Line {
-            color: palette.primary.strong.color,
-            width: 2.0,
-        })
+                Some(pane_grid::Line {
+                    color: palette.primary.strong.color,
+                    width: 2.0,
+                })
+            }
+            PaneGrid::Custom(custom) => custom.picked_split(self),
+        }
     }
 
-    fn hovered_split(&self, _style: Self::Style) -> Option<pane_grid::Line> {
-        let palette = self.extended_palette();
+    fn hovered_split(&self, style: &Self::Style) -> Option<pane_grid::Line> {
+        match style {
+            PaneGrid::Default => {
+                let palette = self.extended_palette();
 
-        Some(pane_grid::Line {
-            color: palette.primary.base.color,
-            width: 2.0,
-        })
+                Some(pane_grid::Line {
+                    color: palette.primary.base.color,
+                    width: 2.0,
+                })
+            }
+            PaneGrid::Custom(custom) => custom.hovered_split(self),
+        }
     }
 }
 
 /*
  * Progress Bar
  */
-#[derive(Clone, Copy)]
 pub enum ProgressBar {
     Primary,
     Success,
     Danger,
-    Custom(fn(&Theme) -> progress_bar::Appearance),
+    Custom(Box<dyn progress_bar::StyleSheet<Style = Theme>>),
 }
 
 impl Default for ProgressBar {
@@ -562,10 +742,20 @@ impl Default for ProgressBar {
     }
 }
 
+impl From<fn(&Theme) -> progress_bar::Appearance> for ProgressBar {
+    fn from(f: fn(&Theme) -> progress_bar::Appearance) -> Self {
+        Self::Custom(Box::new(f))
+    }
+}
+
 impl progress_bar::StyleSheet for Theme {
     type Style = ProgressBar;
 
-    fn appearance(&self, style: Self::Style) -> progress_bar::Appearance {
+    fn appearance(&self, style: &Self::Style) -> progress_bar::Appearance {
+        if let ProgressBar::Custom(custom) = style {
+            return custom.appearance(self);
+        }
+
         let palette = self.extended_palette();
 
         let from_palette = |bar: Color| progress_bar::Appearance {
@@ -578,18 +768,25 @@ impl progress_bar::StyleSheet for Theme {
             ProgressBar::Primary => from_palette(palette.primary.base.color),
             ProgressBar::Success => from_palette(palette.success.base.color),
             ProgressBar::Danger => from_palette(palette.danger.base.color),
-            ProgressBar::Custom(f) => f(self),
+            ProgressBar::Custom(custom) => custom.appearance(self),
         }
     }
 }
 
+impl progress_bar::StyleSheet for fn(&Theme) -> progress_bar::Appearance {
+    type Style = Theme;
+
+    fn appearance(&self, style: &Self::Style) -> progress_bar::Appearance {
+        (self)(style)
+    }
+}
+
 /*
  * Rule
  */
-#[derive(Clone, Copy)]
 pub enum Rule {
     Default,
-    Custom(fn(&Theme) -> rule::Appearance),
+    Custom(Box<dyn rule::StyleSheet<Style = Theme>>),
 }
 
 impl Default for Rule {
@@ -598,10 +795,16 @@ impl Default for Rule {
     }
 }
 
+impl From<fn(&Theme) -> rule::Appearance> for Rule {
+    fn from(f: fn(&Theme) -> rule::Appearance) -> Self {
+        Self::Custom(Box::new(f))
+    }
+}
+
 impl rule::StyleSheet for Theme {
     type Style = Rule;
 
-    fn style(&self, style: Self::Style) -> rule::Appearance {
+    fn appearance(&self, style: &Self::Style) -> rule::Appearance {
         let palette = self.extended_palette();
 
         match style {
@@ -611,48 +814,80 @@ impl rule::StyleSheet for Theme {
                 radius: 0.0,
                 fill_mode: rule::FillMode::Full,
             },
-            Rule::Custom(f) => f(self),
+            Rule::Custom(custom) => custom.appearance(self),
         }
     }
 }
 
+impl rule::StyleSheet for fn(&Theme) -> rule::Appearance {
+    type Style = Theme;
+
+    fn appearance(&self, style: &Self::Style) -> rule::Appearance {
+        (self)(style)
+    }
+}
+
 /*
  * Scrollable
  */
+#[derive(Default)]
+pub enum Scrollable {
+    #[default]
+    Default,
+    Custom(Box<dyn scrollable::StyleSheet<Style = Theme>>),
+}
+
 impl scrollable::StyleSheet for Theme {
-    type Style = ();
+    type Style = Scrollable;
 
-    fn active(&self, _style: Self::Style) -> scrollable::Scrollbar {
-        let palette = self.extended_palette();
+    fn active(&self, style: &Self::Style) -> scrollable::Scrollbar {
+        match style {
+            Scrollable::Default => {
+                let palette = self.extended_palette();
 
-        scrollable::Scrollbar {
-            background: palette.background.weak.color.into(),
-            border_radius: 2.0,
-            border_width: 0.0,
-            border_color: Color::TRANSPARENT,
-            scroller: scrollable::Scroller {
-                color: palette.background.strong.color,
-                border_radius: 2.0,
-                border_width: 0.0,
-                border_color: Color::TRANSPARENT,
-            },
+                scrollable::Scrollbar {
+                    background: palette.background.weak.color.into(),
+                    border_radius: 2.0,
+                    border_width: 0.0,
+                    border_color: Color::TRANSPARENT,
+                    scroller: scrollable::Scroller {
+                        color: palette.background.strong.color,
+                        border_radius: 2.0,
+                        border_width: 0.0,
+                        border_color: Color::TRANSPARENT,
+                    },
+                }
+            }
+            Scrollable::Custom(custom) => custom.active(self),
         }
     }
 
-    fn hovered(&self, _style: Self::Style) -> scrollable::Scrollbar {
-        let palette = self.extended_palette();
+    fn hovered(&self, style: &Self::Style) -> scrollable::Scrollbar {
+        match style {
+            Scrollable::Default => {
+                let palette = self.extended_palette();
 
-        scrollable::Scrollbar {
-            background: palette.background.weak.color.into(),
-            border_radius: 2.0,
-            border_width: 0.0,
-            border_color: Color::TRANSPARENT,
-            scroller: scrollable::Scroller {
-                color: palette.primary.strong.color,
-                border_radius: 2.0,
-                border_width: 0.0,
-                border_color: Color::TRANSPARENT,
-            },
+                scrollable::Scrollbar {
+                    background: palette.background.weak.color.into(),
+                    border_radius: 2.0,
+                    border_width: 0.0,
+                    border_color: Color::TRANSPARENT,
+                    scroller: scrollable::Scroller {
+                        color: palette.primary.strong.color,
+                        border_radius: 2.0,
+                        border_width: 0.0,
+                        border_color: Color::TRANSPARENT,
+                    },
+                }
+            }
+            Scrollable::Custom(custom) => custom.hovered(self),
+        }
+    }
+
+    fn dragging(&self, style: &Self::Style) -> scrollable::Scrollbar {
+        match style {
+            Scrollable::Default => self.hovered(style),
+            Scrollable::Custom(custom) => custom.dragging(self),
         }
     }
 }
@@ -664,7 +899,6 @@ impl scrollable::StyleSheet for Theme {
 pub enum Text {
     Default,
     Color(Color),
-    Custom(fn(&Theme) -> text::Appearance),
 }
 
 impl Default for Text {
@@ -686,7 +920,6 @@ impl text::StyleSheet for Theme {
         match style {
             Text::Default => Default::default(),
             Text::Color(c) => text::Appearance { color: Some(c) },
-            Text::Custom(f) => f(self),
         }
     }
 }
@@ -694,10 +927,21 @@ impl text::StyleSheet for Theme {
 /*
  * Text Input
  */
+#[derive(Default)]
+pub enum TextInput {
+    #[default]
+    Default,
+    Custom(Box<dyn text_input::StyleSheet<Style = Theme>>),
+}
+
 impl text_input::StyleSheet for Theme {
-    type Style = ();
+    type Style = TextInput;
+
+    fn active(&self, style: &Self::Style) -> text_input::Appearance {
+        if let TextInput::Custom(custom) = style {
+            return custom.active(self);
+        }
 
-    fn active(&self, _style: Self::Style) -> text_input::Appearance {
         let palette = self.extended_palette();
 
         text_input::Appearance {
@@ -708,7 +952,11 @@ impl text_input::StyleSheet for Theme {
         }
     }
 
-    fn hovered(&self, _style: Self::Style) -> text_input::Appearance {
+    fn hovered(&self, style: &Self::Style) -> text_input::Appearance {
+        if let TextInput::Custom(custom) = style {
+            return custom.hovered(self);
+        }
+
         let palette = self.extended_palette();
 
         text_input::Appearance {
@@ -719,7 +967,11 @@ impl text_input::StyleSheet for Theme {
         }
     }
 
-    fn focused(&self, _style: Self::Style) -> text_input::Appearance {
+    fn focused(&self, style: &Self::Style) -> text_input::Appearance {
+        if let TextInput::Custom(custom) = style {
+            return custom.focused(self);
+        }
+
         let palette = self.extended_palette();
 
         text_input::Appearance {
@@ -730,19 +982,31 @@ impl text_input::StyleSheet for Theme {
         }
     }
 
-    fn placeholder_color(&self, _style: Self::Style) -> Color {
+    fn placeholder_color(&self, style: &Self::Style) -> Color {
+        if let TextInput::Custom(custom) = style {
+            return custom.placeholder_color(self);
+        }
+
         let palette = self.extended_palette();
 
         palette.background.strong.color
     }
 
-    fn value_color(&self, _style: Self::Style) -> Color {
+    fn value_color(&self, style: &Self::Style) -> Color {
+        if let TextInput::Custom(custom) = style {
+            return custom.value_color(self);
+        }
+
         let palette = self.extended_palette();
 
         palette.background.base.text
     }
 
-    fn selection_color(&self, _style: Self::Style) -> Color {
+    fn selection_color(&self, style: &Self::Style) -> Color {
+        if let TextInput::Custom(custom) = style {
+            return custom.selection_color(self);
+        }
+
         let palette = self.extended_palette();
 
         palette.primary.weak.color
diff --git a/style/src/toggler.rs b/style/src/toggler.rs
index 0acf8e97..fcc7e45b 100644
--- a/style/src/toggler.rs
+++ b/style/src/toggler.rs
@@ -12,9 +12,9 @@ pub struct Appearance {
 
 /// A set of rules that dictate the style of a toggler.
 pub trait StyleSheet {
-    type Style: Default + Copy;
+    type Style: Default;
 
-    fn active(&self, style: Self::Style, is_active: bool) -> Appearance;
+    fn active(&self, style: &Self::Style, is_active: bool) -> Appearance;
 
-    fn hovered(&self, style: Self::Style, is_active: bool) -> Appearance;
+    fn hovered(&self, style: &Self::Style, is_active: bool) -> Appearance;
 }
diff --git a/winit/src/application/state.rs b/winit/src/application/state.rs
index 9c539548..8d6a1df1 100644
--- a/winit/src/application/state.rs
+++ b/winit/src/application/state.rs
@@ -32,7 +32,7 @@ where
         let title = application.title();
         let scale_factor = application.scale_factor();
         let theme = application.theme();
-        let appearance = theme.appearance(application.style());
+        let appearance = theme.appearance(&application.style());
 
         let viewport = {
             let physical_size = window.inner_size();
@@ -210,6 +210,6 @@ where
 
         // Update theme and appearance
         self.theme = application.theme();
-        self.appearance = self.theme.appearance(application.style());
+        self.appearance = self.theme.appearance(&application.style());
     }
 }