Undo and redo

Changes are kept per document, so undo and redo act on the document you are working in.

Undo: Ctrl+Z (Cmd+Z on a Mac).
Redo: Ctrl+Shift+Z (Cmd+Shift+Z on a Mac).
Both are also available by name in the command palette: Run a command.
One edit made in the Properties panel panel, or one gesture in a view, is one undo step. A command that changes several things at once is undone in one step too.