It's weird that this shortcut only works if a cell is focused. Shouldn't the pane also appear when nothing is in focus (or if a rendered html word is "selected")?

Shift-Command-F doesn’t require a cell to be focused, but it does require the Observable editor/application to be focused rather than the sandboxed (“worker“) iframe which runs user code. So if you’ve clicked on the output of a cell, the worker iframe receives focus and the Observable editor can no longer intercept key events. You can read more about our security model here: https://observablehq.com/@observablehq/security-model When the worker iframe has focus, you can hit Esc to restore focus to the Observable editor. So if you ever find that Shift-Command-F doesn’t work, hit Esc once (or twice) and try again.