message: Center contents with `Container` in `exit` example
  ... also add some `padding` to buttons!
diff: use iced::{
  - button, Alignment, Button, Column, Element, Sandbox, Settings, Text,
  + button, Alignment, Button, Column, Container, Element, Length, Sandbox,
  + Settings, Text,
  };
  pub fn main() -> iced::Result {
  @@ -47,9 +48,9 @@ impl Sandbox for Exit {
  }
  fn view(&mut self) -> Element<Message> {
  - if self.show_confirm {
  + let content = if self.show_confirm {
  Column::new()
  - .padding(20)
  + .spacing(10)
  .align_items(Alignment::Center)
  .push(Text::new("Are you sure you want to exit?"))
  .push(
  @@ -57,19 +58,27 @@ impl Sandbox for Exit {
  &mut self.confirm_button,
  Text::new("Yes, exit now"),
  )
  + .padding([10, 20])
  .on_press(Message::Confirm),
  )
  - .into()
  } else {
  Column::new()
  - .padding(20)
  + .spacing(10)
  .align_items(Alignment::Center)
  .push(Text::new("Click the button to exit"))
  .push(
  Button::new(&mut self.exit_button, Text::new("Exit"))
  + .padding([10, 20])
  .on_press(Message::Exit),
  )
  + };
  +
  + Container::new(content)
  + .width(Length::Fill)
  + .height(Length::Fill)
  + .padding(20)
  + .center_x()
  + .center_y()
  .into()
  }
  }
  -}
  