refactor Sidebar into own file

Sidebar.py

@@ -0,0 +1,31 @@
+from textual.containers import Container
+from textual.app import ComposeResult
+from textual.widgets import Static, Button
+
+MESSAGE = '''
+Be excellent to each other!
+
+Made with :red_heart: by Panki
+
+[@click="app.open_link('https://tty0.social/@panki')"]Mastodon:[/] tty0.social/@panki
+[@click="app.open_link('https://git.theresno.cloud/panki/bingo-cli')"]Source:[/] git.theresno.cloud/panki/bingo-cli
+
+Built using [@click="app.open_link('https://textual.textualize.io/')"]Textual[/]
+
+'''
+
+class Sidebar(Container):
+    '''Class to represent the sidebar'''
+
+    def compose(self) -> ComposeResult:
+        '''Create the widgets that make up the sidebar'''
+        yield Static('CCC Bingo', classes='title')
+        yield Static(MESSAGE, classes='message')
+        self.button = Button('< Back', variant='primary', classes='btn_sidebar')
+        self.button.disabled = True
+        yield self.button
+
+    def on_button_pressed(self, event: Button.Pressed) -> None:
+        '''Closes the sidebar'''
+        self.app.action_toggle_sidebar()
+

bingo.py

@@ -2,7 +2,7 @@
 
 from textual.app import App, ComposeResult
 from textual.widgets import Header, Input, Static, Button 
-from textual.containers import Horizontal, Container
+from textual.containers import Horizontal
 from textual.validation import Number
 from textual.reactive import reactive
 
@@ -10,33 +10,7 @@ from datetime import datetime
 
 from BingoBoard import BingoBoard
 from AboutCommand import AboutCommand
-
-MESSAGE = '''
-Be excellent to each other!
-
-Made with :red_heart: by Panki
-
-[@click="app.open_link('https://tty0.social/@panki')"]Mastodon:[/] tty0.social/@panki
-[@click="app.open_link('https://git.theresno.cloud/panki/bingo-cli')"]Source:[/] git.theresno.cloud/panki/bingo-cli
-
-Built using [@click="app.open_link('https://textual.textualize.io/')"]Textual[/]
-
-'''
-
-class Sidebar(Container):
-    '''Class to represent the sidebar'''
-
-    def compose(self) -> ComposeResult:
-        '''Create the widgets that make up the sidebar'''
-        yield Static('CCC Bingo', classes='title')
-        yield Static(MESSAGE, classes='message')
-        self.button = Button('< Back', variant='primary', classes='btn_sidebar')
-        self.button.disabled = True
-        yield self.button
-
-    def on_button_pressed(self, event: Button.Pressed) -> None:
-        '''Closes the sidebar'''
-        self.app.action_toggle_sidebar()
+from Sidebar import Sidebar
 
 class BingoApp(App):
     '''