Remove default styling of Button

- A background will only show if explicitly set.
- `iced_wgpu` won't apply a `min_width` of 100 units anymore.

examples/tour.rs

@@ -671,6 +671,7 @@ fn button<'a, Message>(
     )
     .padding(12)
     .border_radius(12)
+    .min_width(100)
 }
 
 fn primary_button<'a, Message>(