Don't expand widgets on hover

crates/egui/src/style.rs

@@ -1234,6 +1234,11 @@ pub struct WidgetVisuals {
     pub fg_stroke: Stroke,
 
     /// Make the frame this much larger.
+    ///
+    /// The problem with "expanding" widgets is that they now want to paint outside their own bounds,
+    /// which then requires all parent UIs to have proper margins.
+    ///
+    /// It also means hovered things are no longer properly aligned with every other widget.
     pub expansion: f32,
 }
 
@@ -1568,15 +1573,15 @@ impl Widgets {
                 bg_stroke: Stroke::new(1.0, Color32::from_gray(150)), // e.g. hover over window edge or button
                 fg_stroke: Stroke::new(1.5, Color32::from_gray(240)),
                 corner_radius: CornerRadius::same(3),
-                expansion: 1.0,
+                expansion: 0.0,
             },
             active: WidgetVisuals {
                 weak_bg_fill: Color32::from_gray(55),
                 bg_fill: Color32::from_gray(55),
                 bg_stroke: Stroke::new(1.0, Color32::WHITE),
                 fg_stroke: Stroke::new(2.0, Color32::WHITE),
                 corner_radius: CornerRadius::same(2),
-                expansion: 1.0,
+                expansion: 0.0,
             },
             open: WidgetVisuals {
                 weak_bg_fill: Color32::from_gray(45),
@@ -1613,15 +1618,15 @@ impl Widgets {
                 bg_stroke: Stroke::new(1.0, Color32::from_gray(105)), // e.g. hover over window edge or button
                 fg_stroke: Stroke::new(1.5, Color32::BLACK),
                 corner_radius: CornerRadius::same(3),
-                expansion: 1.0,
+                expansion: 0.0,
             },
             active: WidgetVisuals {
                 weak_bg_fill: Color32::from_gray(165),
                 bg_fill: Color32::from_gray(165),
                 bg_stroke: Stroke::new(1.0, Color32::BLACK),
                 fg_stroke: Stroke::new(2.0, Color32::BLACK),
                 corner_radius: CornerRadius::same(2),
-                expansion: 1.0,
+                expansion: 0.0,
             },
             open: WidgetVisuals {
                 weak_bg_fill: Color32::from_gray(220),