message: Use `Palette` consistently in `arc` example
diff: @@ -5,9 +5,7 @@ use iced::pure::widget::canvas::{
  self, Cache, Canvas, Cursor, Geometry, Path, Stroke,
  };
  use iced::pure::{Application, Element};
  -use iced::{
  - Color, Command, Length, Point, Rectangle, Settings, Subscription, Theme,
  -};
  +use iced::{Command, Length, Point, Rectangle, Settings, Subscription, Theme};
  pub fn main() -> iced::Result {
  Arc::run(Settings {
  @@ -80,6 +78,8 @@ impl<Message> canvas::Program<Message> for Arc {
  _cursor: Cursor,
  ) -> Vec<Geometry> {
  let geometry = self.cache.draw(bounds.size(), |frame| {
  + let palette = theme.palette();
  +
  let center = frame.center();
  let radius = frame.width().min(frame.height()) / 5.0;
  @@ -101,7 +101,7 @@ impl<Message> canvas::Program<Message> for Arc {
  b.circle(end, 10.0);
  });
  - frame.fill(&circles, Color::WHITE);
  + frame.fill(&circles, palette.text);
  let path = Path::new(|b| {
  b.move_to(start);
  @@ -109,8 +109,6 @@ impl<Message> canvas::Program<Message> for Arc {
  b.line_to(end);
  });
  - let palette = theme.palette();
  -
  frame.stroke(
  &path,
  Stroke {
  