I am using `Popup` widgets in `python-2.7` and `kivy`.Can someone help me?  

1. How to make label bold ? (ex. `text: "make label bold"`)  

2. How to change color of title ? (ex. `title : "change title color"`)

test.py
=======

```
from kivy.app import App
from kivy.core.window import Window
from kivy.uix.popup import Popup

class abc(Popup):
    def __init__(self, **kwargs):
        super(abc, self).__init__(**kwargs)
        self.open()

class TestApp(App):
    def build(self):
        return abc()

TestApp().run()

```

test.kv
=======

```
<abc>
    title : "change title color"
    BoxLayout:
        orientation: "vertical"
        GridLayout:
            Label:
                text: "make label bold"

```