fix: exclude scroll area padding from pane sizing

crates/core/src/scroll_area.rs

@@ -222,6 +222,9 @@ pub(crate) fn thumb_geometry(
 
 impl RenderOnce for ScrollArea {
     fn render(self, _window: &mut Window, cx: &mut App) -> impl IntoElement {
+        let mut pane_style = self.style.clone();
+        pane_style.padding = Default::default();
+
         let mut pane = div()
             .id(self.id.clone())
             .overflow_hidden()
@@ -239,7 +242,7 @@ impl RenderOnce for ScrollArea {
                 // Keep wheel events from scrolling an outer scroll area too.
                 cx.stop_propagation();
             })
-            .refine_style(&self.style);
+            .refine_style(&pane_style);
 
         // Extend with children
         pane.extend(self.children);
@@ -248,17 +251,18 @@ impl RenderOnce for ScrollArea {
         wrapper.extend(std::iter::once(pane.into_any_element()));
 
         if let Some(handle) = self.handle {
+            let id = self.id.clone();
             let autohide = match self.visibility {
                 ScrollbarVisibility::Platform => cx.theme().scrollbar.autohide,
                 ScrollbarVisibility::Always => false,
                 ScrollbarVisibility::Autohide => true,
             };
-            let id = self.id.clone();
+
             wrapper.extend(std::iter::once(
-                canvas(|_, _, _| {}, {
+                canvas(|bounds, _, _| bounds, {
                     let handle = handle.clone();
-                    move |_, _, window, cx| {
-                        paint_scrollbar(&handle, &id, autohide, window, cx);
+                    move |overlay, _, window, cx| {
+                        paint_scrollbar(&handle, &id, autohide, overlay, window, cx);
                     }
                 })
                 .absolute()
@@ -276,6 +280,7 @@ fn paint_scrollbar(
     handle: &ScrollHandle,
     key: &ElementId,
     autohide: bool,
+    overlay: Bounds<Pixels>,
     window: &mut Window,
     cx: &mut App,
 ) {
@@ -287,10 +292,10 @@ fn paint_scrollbar(
     let inset = theme.scrollbar.inset;
     let min_thumb = theme.scrollbar.min_thumb;
 
+    let viewport = handle.bounds();
     let max_offset = handle.max_offset().y;
-    let bounds = handle.bounds();
 
-    if max_offset <= Pixels::ZERO || bounds.size.height <= Pixels::ZERO {
+    if max_offset <= Pixels::ZERO || viewport.size.height <= Pixels::ZERO {
         return;
     }
 
@@ -306,21 +311,21 @@ fn paint_scrollbar(
         _ => 1.0,
     };
 
-    let track = bounds.size.height - inset * 2.0;
+    let track = overlay.size.height - inset * 2.0;
     let (thumb_length, thumb_top) = thumb_geometry(
-        bounds.size.height,
-        bounds.size.height + max_offset,
+        viewport.size.height,
+        viewport.size.height + max_offset,
         handle.offset().y,
         track,
         min_thumb,
     );
 
-    let thumb_x = bounds.right() - width - inset;
+    let thumb_x = overlay.right() - width - inset;
     let thumb_bounds = Bounds::from_corners(
-        point(thumb_x, bounds.top() + inset + thumb_top),
+        point(thumb_x, overlay.top() + inset + thumb_top),
         point(
             thumb_x + width,
-            bounds.top() + inset + thumb_top + thumb_length,
+            overlay.top() + inset + thumb_top + thumb_length,
         ),
     );
 
@@ -332,7 +337,7 @@ fn paint_scrollbar(
         window.on_mouse_event({
             let state = state.clone();
             move |event: &ScrollEvent, phase, window, cx| {
-                if phase != DispatchPhase::Bubble || !bounds.contains(&event.position) {
+                if phase != DispatchPhase::Bubble || !overlay.contains(&event.position) {
                     return;
                 }
                 state.touch(window, cx);