Add some more helpers

crates/egui/src/class/has_classes.rs

@@ -108,6 +108,17 @@ pub trait HasClasses {
     fn classes_as_slice(&self) -> &[ClassName] {
         self.classes().as_slice()
     }
+
+    /// The last class that names a `T`, if any.
+    ///
+    /// Scanning backwards is what makes the last class win, so a widget given two classes of the
+    /// same kind takes the one set last — the way a later stylesheet rule overrides an earlier one.
+    fn last_class<T>(&self, from_class_name: impl Fn(&str) -> Option<T>) -> Option<T> {
+        self.classes_as_slice()
+            .iter()
+            .rev()
+            .find_map(|class| from_class_name(class))
+    }
 }
 
 #[cfg(test)]

crates/egui/src/ui_stack.rs

@@ -295,6 +295,15 @@ impl UiStack {
     pub fn has_class(&self, class: &str) -> bool {
         self.iter().any(|node| node.classes.has_class(class))
     }
+
+    /// Read a value from the classes up the stack, nearest node first.
+    ///
+    /// This is how an inherited property works in a stylesheet: a container states it once, and
+    /// everything inside picks it up. The nearest [`crate::Ui`] wins, so an inner container can
+    /// override an outer one.
+    pub fn inherited<T>(&self, from_classes: impl Fn(&Classes) -> Option<T>) -> Option<T> {
+        self.iter().find_map(|node| from_classes(&node.classes))
+    }
 }
 
 // ----------------------------------------------------------------------------

crates/egui/src/widget_style/mod.rs

@@ -228,4 +228,11 @@ impl StyleArgs<'_> {
     pub fn has_class(&self, class: &str) -> bool {
         self.classes.has_class(class) || self.stack.has_class(class)
     }
+
+    /// Read a value from the widget's own classes, falling back to the [`crate::Ui`]s it sits in.
+    ///
+    /// See [`UiStack::inherited`] for how the fallback resolves.
+    pub fn inherited<T>(&self, from_classes: impl Fn(&Classes) -> Option<T>) -> Option<T> {
+        from_classes(self.classes).or_else(|| self.stack.inherited(from_classes))
+    }
 }