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

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)]

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 {

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;
 }

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;
 }

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;
 }

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.

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;
 }

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;
 }

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;
 }

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.

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)
     }
 }

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;
 }

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)
     }
 }

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
  */
+#[derive(Default)]
+pub enum Slider {
+    #[default]
+    Default,
+    Custom(Box<dyn slider::StyleSheet<Style = Theme>>),
+}
+
 impl slider::StyleSheet for Theme {
-    type Style = ();
+    type Style = Slider;
 
-    fn active(&self, _style: Self::Style) -> slider::Appearance {
-        let palette = self.extended_palette();
+    fn active(&self, style: &Self::Style) -> slider::Appearance {
+        match style {
+            Slider::Default => {
+                let palette = self.extended_palette();
 
-        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,
-        };
+                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::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
  */
-impl text_input::StyleSheet for Theme {
-    type Style = ();
+#[derive(Default)]
+pub enum TextInput {
+    #[default]
+    Default,
+    Custom(Box<dyn text_input::StyleSheet<Style = Theme>>),
+}
+
+impl text_input::StyleSheet for Theme {
+    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

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;
 }