message: Use `Theme` background in `styling` example
diff: @@ -147,7 +147,6 @@ impl Sandbox for Styling {
  .height(Length::Fill)
  .center_x()
  .center_y()
  - .style(self.theme)
  .into()
  }
  @@ -160,9 +159,7 @@ impl Sandbox for Styling {
  }
  mod style {
  - use iced::{
  - checkbox, container, progress_bar, rule, scrollable, text_input,
  - };
  + use iced::{checkbox, progress_bar, rule, scrollable, text_input};
  #[derive(Debug, Clone, Copy, PartialEq, Eq)]
  pub enum Theme {
  @@ -180,15 +177,6 @@ mod style {
  }
  }
  - impl<'a> From<Theme> for Box<dyn container::StyleSheet + 'a> {
  - fn from(theme: Theme) -> Self {
  - match theme {
  - Theme::Light => Default::default(),
  - Theme::Dark => dark::Container.into(),
  - }
  - }
  - }
  -
  impl<'a> From<Theme> for Box<dyn text_input::StyleSheet + 'a> {
  fn from(theme: Theme) -> Self {
  match theme {
  @@ -236,8 +224,7 @@ mod style {
  mod dark {
  use iced::{
  - checkbox, container, progress_bar, rule, scrollable, text_input,
  - Color,
  + checkbox, progress_bar, rule, scrollable, text_input, Color,
  };
  const SURFACE: Color = Color::from_rgb(
  @@ -264,18 +251,6 @@ mod style {
  0xC4 as f32 / 255.0,
  );
  - pub struct Container;
  -
  - impl container::StyleSheet for Container {
  - fn style(&self) -> container::Style {
  - container::Style {
  - background: Color::from_rgb8(0x36, 0x39, 0x3F).into(),
  - text_color: Color::WHITE.into(),
  - ..container::Style::default()
  - }
  - }
  - }
  -
  pub struct TextInput;
  impl text_input::StyleSheet for TextInput {
  