Add modifier for window devel style

Sources/Adwaita/Window/Window.swift

@@ -43,6 +43,8 @@ public struct Window: WindowScene {
     var setDefaultSize = false
     /// Whether the window is maximized.
     var maximized: Binding<Bool>?
+    /// Whether the window uses the development style.
+    var devel = false
 
     /// Create a window type with a certain identifier and user interface.
     /// - Parameters:
@@ -66,6 +68,9 @@ public struct Window: WindowScene {
             windowStorage.destroy = true
         }
         windowStorage.parentID = parentID
+        if devel {
+            gtk_widget_add_css_class(window.pointer?.cast(), "devel")
+        }
         return windowStorage
     }
 
@@ -341,6 +346,15 @@ public struct Window: WindowScene {
         return newSelf
     }
 
+    /// Whether the window used the development style.
+    /// - Parameter active: Whether the style is active.
+    /// - Returns: The window.
+    public func devel(_ active: Bool = true) -> Self {
+        var newSelf = self
+        newSelf.devel = active
+        return newSelf
+    }
+
 }
 
 // swiftlint:enable discouraged_optional_collection

Tests/Demo.swift

@@ -22,6 +22,7 @@ struct Demo: App {
         Window(id: "main") { window in
             DemoContent(window: window, app: app, pictureURL: pictureURL)
         }
+        .devel()
         HelperWindows()
         FileDialog(importer: "picture", extensions: ["jpg", "jpeg", "png", "svg"]) { pictureURL = $0 } onClose: { }
     }