title: Variables in Kv language (kivy)
body: <p>My Kivy Language file has many font_size properties, all with same values, is there away where I can assign a variable in KV lang?
  Current KV file sample:</p>
  
  <pre><code>#User ID
      Label:
          text: 'User ID'
          font_size: 20
          text_size: self.size
  
      TextInput:
          id: userid
          font_size: 20
  
  
      #User PW
      Label:
          text: 'Password'
          font_size: 20
          text_size: self.size
  
      TextInput:
          id: password
          password: True
          font_size: 20
  
      Button:
          text: 'Login'
          font_size: 20
  </code></pre>
  
  <p>Is is possible to set it somewhat like this:</p>
  
  <pre><code>#User ID
      @fs: 20
      Label:
          text: 'User ID'
          font_size: fs
          text_size: self.size
  
      TextInput:
      id: userid
      font_size: fs
  
  
  #User PW
  Label:
      text: 'Password'
      font_size: fs
      text_size: self.size
  
  TextInput:
      id: password
      password: True
      font_size: fs
  
  Button:
      text: 'Login'
      font_size: fs
  </code></pre>
  
  <p>By doing so, I would be able to change the font size at once only by changing the FS variable value, also, similar solution might help me to create theme based files faster.  Thank you.</p>