Undo available also as an icon

[jangenoe]

Zotero-better-notes supports "undo" as Ctrl+Z.
The same holds for copy Ctrl+C and paste Ctrl+V

It would be nice to have this undo also as an icon on the top bar, besides the existing icons

It would be even nicer if this undo would change color when an undo option is available, as is the case in Notepad++.
As an example:

• Undo and paste are available:
  
• No undo and paste are available but Cut and copy available, i.e. a part of the note is selected:
  

If you want to limit real-estate on the top bar, only the undo would already be a great option.