ui: Update Label component (#24653)

- Standardize style methods
- Convert label story to a component preview
- update component preview styles  

Release Notes:

- N/A

crates/repl/src/notebook/notebook_ui.rs

@@ -738,7 +738,7 @@ impl Item for NotebookEditor {
         Label::new(title)
             .single_line()
             .color(params.text_color())
-            .italic(params.preview)
+            .when(params.preview, |this| this.italic())
             .into_any_element()
     }