feat: add overlay option to appearance for vertical icon button

src/widget/button/style.rs

@@ -16,6 +16,9 @@ pub struct Appearance {
     /// The [`Background`] of the button.
     pub background: Option<Background>,
 
+    /// The [`Background`] overlay of the button.
+    pub overlay: Option<Background>,
+
     /// The border radius of the button.
     pub border_radius: Radius,
 
@@ -52,6 +55,7 @@ impl Appearance {
             outline_color: Color::TRANSPARENT,
             icon_color: None,
             text_color: None,
+            overlay: None,
         }
     }
 }

src/widget/button/widget.rs

@@ -813,6 +813,21 @@ pub fn draw<Renderer: iced_core::Renderer, Theme>(
             );
         }
 
+        // Then button overlay if any.
+        if let Some(overlay) = styling.overlay {
+            renderer.fill_quad(
+                renderer::Quad {
+                    bounds,
+                    border: Border {
+                        radius: styling.border_radius,
+                        ..Default::default()
+                    },
+                    shadow: Shadow::default(),
+                },
+                overlay,
+            );
+        }
+
         // Then draw the button contents onto the background.
         draw_contents(renderer, styling);