Implement `Widget::overlay` for `Scrollable`

examples/combo_box/src/main.rs

@@ -1,6 +1,6 @@
 use iced::{
-    button, combo_box, Button, Column, ComboBox, Container, Element, Length,
-    Sandbox, Settings, Text,
+    button, combo_box, scrollable, Align, Button, ComboBox, Container, Element,
+    Length, Sandbox, Scrollable, Settings, Space, Text,
 };
 
 pub fn main() {
@@ -9,6 +9,7 @@ pub fn main() {
 
 #[derive(Default)]
 struct Example {
+    scroll: scrollable::State,
     button: button::State,
     combo_box: combo_box::State,
     selected_language: Language,
@@ -51,8 +52,11 @@ impl Sandbox for Example {
         let button = Button::new(&mut self.button, Text::new("Press me!"))
             .on_press(Message::ButtonPressed);
 
-        let mut content = Column::new()
+        let mut content = Scrollable::new(&mut self.scroll)
+            .width(Length::Fill)
+            .align_items(Align::Center)
             .spacing(10)
+            .push(Space::with_height(Length::Units(800)))
             .push(Text::new("Which is your favorite language?"))
             .push(combo_box);
 
@@ -60,7 +64,9 @@ impl Sandbox for Example {
             content = content.push(Text::new("You are wrong!"));
         }
 
-        content = content.push(button);
+        content = content
+            .push(button)
+            .push(Space::with_height(Length::Units(800)));
 
         Container::new(content)
             .width(Length::Fill)

native/src/widget/scrollable.rs

@@ -1,7 +1,7 @@
 //! Navigate an endless amount of content with a scrollbar.
 use crate::{
     column, layout, mouse, Align, Clipboard, Column, Element, Event, Hasher,
-    Layout, Length, Point, Rectangle, Size, Widget,
+    Layout, Length, Overlay, Point, Rectangle, Size, Vector, Widget,
 };
 
 use std::{f32, hash::Hash, u32};
@@ -315,6 +315,22 @@ where
 
         self.content.hash_layout(state)
     }
+
+    fn overlay(
+        &mut self,
+        layout: Layout<'_>,
+    ) -> Option<Overlay<'a, Message, Renderer>> {
+        self.content
+            .overlay(layout.children().next().unwrap())
+            .map(|overlay| {
+                let bounds = layout.bounds();
+                let content_layout = layout.children().next().unwrap();
+                let content_bounds = content_layout.bounds();
+                let offset = self.state.offset(bounds, content_bounds);
+
+                overlay.translate(Vector::new(0.0, -(offset as f32)))
+            })
+    }
 }
 
 /// The local state of a [`Scrollable`].