Description : When adding a style that includes formatting (for example, Bold, Heading, or custom styles) in Excel, using Undo (Ctrl+Z) does not undo the adding of the style. It only undoes the formatting portion. If multiple styles are added, Undo only partially reverts the formatting, while the style itself remains added/applied. See related issue: https://github.com/OfficeDev/office-js/issues/5995
Impact In scenarios where styles are checked only by name (without validating their properties), the current Undo behavior causes issues: it resets style properties but keeps the style itself, leading to inconsistencies in the worksheet. When multiple styles are applied, Undo only partially reverts formatting, leaving a mix of styles that creates further inconsistency.
Suggestion Treat adding and applying a style as a single, complete action in the Undo/Redo stack. This way, Undo fully removes the style and all its formatting, ensuring consistent behavior even when one or multiple styles are applied.