change item to rectangle

doric-Qt/doric/resources/Flex.qml

@@ -2,7 +2,7 @@ import QtQuick 2.12
 import QtQuick.Layouts 1.15
 import pub.doric.widget 1.0
 
-Item {
+Rectangle {
     id: flex
 
     property int minHeight: 0

doric-demo/src/SimpleDemo.ts

@@ -65,7 +65,7 @@ class LayoutDemo extends Panel {
                 height: 300,
             })
         ], {
-            width: 300,
+            width: 400,
             height: 300,
             backgroundColor: Color.BLACK
         }).in(rootView)