title: Is there a simple way to add a border to Kivy Labels, Buttons, Widgets etc. with-out images?
body: <p>I'm trying to add a border to Kivy Buttons but it doesn't work as expected.
  For labels my implementation seems to be OK but for buttons it overrides/clears the standard look of the button.</p>
  
  <p>How can I draw the border above the button with-out changing normal behavior? I'd like to implement it like the ButtonBehavior so I can add a border to every Kivy object with a canvas. I've called it BorderBehavior.</p>
  
  <p>Styling dashed, dotted works only for line width of 1 because there is a bug in Kivy (see <a href="https://github.com/kivy/kivy/issues/2037" rel="noreferrer">https://github.com/kivy/kivy/issues/2037</a>) (Need to figure out what's wrong here later.)</p>
  
  <p>I know that drawing a border is possible with a BorderImage but I'd like to add simple borders with-out an image.</p>
  
  <p>Here is how it looks at the moment:
  <img src="https://i.stack.imgur.com/M49tI.gif" alt="Screenshot of border demo app"></p>
  
  <p>You can find my source code here (the labels can be dragged just for testing purposes to see that the border is always correctly positioned):</p>
  
  <p><a href="https://gist.github.com/AWolf81/c6796dc2049d9872b2df" rel="noreferrer">https://gist.github.com/AWolf81/c6796dc2049d9872b2df</a></p>