Method begin_theme_preview

src/apps/cli/src/ui/startup.rs:1700–1704

(&mut self)

    }

    fn begin_theme_preview(&mut self) {
        if self.theme_preview_original.is_none() {
            self.theme_preview_original = Some(self.theme.clone());
        }
    }

    fn cancel_theme_preview(&mut self) {
        if let Some(original) = self.theme_preview_original.take() {