message: Implement `Default` for `Theme` in `styling` example
diff: @@ -7,6 +7,7 @@ pub fn main() {
  Styling::run(Settings::default())
  }
  +#[derive(Default)]
  struct Styling {
  theme: style::Theme,
  input: text_input::State,
  @@ -25,12 +26,7 @@ impl Sandbox for Styling {
  type Message = Message;
  fn new() -> Self {
  - Styling {
  - theme: style::Theme::Light,
  - input: text_input::State::default(),
  - input_value: String::new(),
  - button: button::State::default(),
  - }
  + Styling::default()
  }
  fn title(&self) -> String {
  @@ -106,6 +102,12 @@ mod style {
  pub const ALL: [Theme; 2] = [Theme::Light, Theme::Dark];
  }
  + impl Default for Theme {
  + fn default() -> Theme {
  + Theme::Light
  + }
  + }
  +
  impl From<Theme> for Box<dyn container::StyleSheet> {
  fn from(theme: Theme) -> Self {
  match theme {
  