Add pane_grid functionality to split a pane with another pane

style/src/pane_grid.rs

@@ -1,11 +1,14 @@
 //! Change the appearance of a pane grid.
-use iced_core::Color;
+use iced_core::{Background, Color};
 
 /// A set of rules that dictate the style of a container.
 pub trait StyleSheet {
     /// The supported style of the [`StyleSheet`].
     type Style: Default;
 
+    /// The [`Region`] to draw when a pane is hovered.
+    fn hovered_region(&self, style: &Self::Style) -> Region;
+
     /// The [`Line`] to draw when a split is picked.
     fn picked_split(&self, style: &Self::Style) -> Option<Line>;
 
@@ -13,6 +16,19 @@ pub trait StyleSheet {
     fn hovered_split(&self, style: &Self::Style) -> Option<Line>;
 }
 
+/// The appearance of the hovered region of a pane grid.
+#[derive(Debug, Clone, Copy)]
+pub struct Region {
+    /// The [`Background`] of the hovered pane region.
+    pub background: Background,
+    /// The border width of the hovered pane region.
+    pub border_width: f32,
+    /// The border [`Color`] of the hovered pane region.
+    pub border_color: Color,
+    /// The border radius of the hovered pane region.
+    pub border_radius: f32,
+}
+
 /// A line.
 ///
 /// It is normally used to define the highlight of something, like a split.