slightly improved structure and added a few more elements

src/element/rect.rs

@@ -0,0 +1,20 @@
+use crate::Element;
+
+pub struct Rect(pub u32);
+impl Element for Rect {
+    fn render(&mut self, scope: &mut crate::render_scope::RenderScope) {
+        let (w, h) = scope.get_size();
+
+        if w > 0 && h > 0 {
+            scope.draw_rect(w, h, self.0);
+        }
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
+        self
+    }
+
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
+}