title: screen not showing widgets
body: <p>my main file . plz teach me what is my mistake, i used screenmanager to navigate between the 2 screen,
  what is problem in my program? it irritating me for past 2 days. while using KIVY it is working , but mixing with kivymd and kivy it just showing black screen without the widgets i added.</p>
  <pre><code>from kivymd.app import MDApp
  from kivy.lang import Builder
  from kivy.uix.screenmanager import ScreenManager,Screen
  
  
  
  
  class login_window(Screen):
      pass
  
  
  class create_acc_window(Screen):
      pass
  
  
  class WindowManager(ScreenManager):
      pass
  
  class DemoApp(MDApp):
      def build(self):
          self.root=Builder.load_file(&quot;my.kv&quot;)
          self.theme_cls.theme_style='Dark'
  
  
  if __name__ =='__main__':
      DemoApp().run()
      enter code herefrom kivymd.app import MDApp
  from kivy.lang import Builder
  from kivy.uix.screenmanager import ScreenManager,Screen
  
  
  
  
  class login_window(Screen):
      pass
  
  
  class create_acc_window(Screen):
      pass
  
  
  class WindowManager(ScreenManager):
      pass
  
  class DemoApp(MDApp):
      def build(self):
          self.root=Builder.load_file(&quot;my.kv&quot;)
          self.theme_cls.theme_style='Dark'
  
  
  if __name__ =='__main__':
      DemoApp().run()
      from kivymd.app import MDApp
  from kivy.lang import Builder
  from kivy.uix.screenmanager import ScreenManager,Screen
  
  
  
  
  class login_window(Screen):
      pass
  
  
  class create_acc_window(Screen):
      pass
  
  
  class WindowManager(ScreenManager):
      pass
  
  class DemoApp(MDApp):
      def build(self):
          self.root=Builder.load_file(&quot;my.kv&quot;)
          self.theme_cls.theme_style='Dark'
  
  
  if __name__ =='__main__':
      DemoApp().run()
  </code></pre>
  <p>my kv language file is</p>
  <pre><code>&lt;WindowManager&gt;:
      login_window:
      crate_acc_window:
      current: 'loginscreen'
  
  &lt;login_window&gt;:
      name : 'loginscreen'
      MDFloatLayout:
          MDTextFieldRound:
              hint_text:'UserName'
              size_hint_x:None
              size:(180,0)
              pos_hint:{'center_x':0.5,'center_y':0.5}
              icon_left:'email'
  
  
          MDTextFieldRound:
              pos_hint:{'center_x':0.5,'center_y':0.4}
              hint_text:'Password'
              size_hint_x: None
              size: (180,0)
              icon_left:'key-variant'
  
          MDRoundFlatIconButton:
              text: 'Log in'
              pos_hint:{'center_x':0.5,'center_y':0.3}
              on_release: app.root.current='secondscreen'
  &lt;create_acc_window&gt;:
      name: 'secondscreen'
      MDFloatLayout:
          MDTextField:
              mode:'rectangle'
              hint_text:'First Name'
              size_hint_x:None
              size:(150,0)
              pos_hint:{'left':0.4,'center_y':0.6}
  
          MDTextField:
              mode:'rectangle'
              hint_text:'Last Name'
              size_hint_x:None
              size:(150,0)
              pos_hint:{'right':0.4,'center_y':0.6}
          MDTextFieldRound:
              hint_text: 'Email'
              size_hint_x:None
              icon_left:'Email'
              size:(180,0)
              pos_hint:{'center_x':0.5,'center_y':0.5}
          MDTextFieldRound:
              hint_text: 'Password'
              size_hint_x:None
              size:(180,0)
              pos_hint:{'center_x':0.5,'center_y':0.5}
          MDTextFieldRound:
              hint_text: 'Renter-Password'
              size_hint_x:None
              size:(180,0)
              pos_hint:{'center_x':0.5,'center_y':0.4}
          MDRoundFlatIconButton:
              text: 'Create'
              on_release: app.root.current='loginscreen'
  </code></pre>
  <p>the output just rendering screen . not showing the widget. plz help me to solve it
  plz.. im stucking here for 2 days. sorry, for my  bad english.</p>