When you press F9 or the “Preview” button in Openbox, the preview spreadsheet window appears.

You can hide or show this window by pressing Ctrl+Shift+P (P for Preview). You can also use the toggle on the menu. Click “View” then the three dots at the end, and then the “Preview” button.

You can resize the window by moving your mouse over the black line at the top of the preview and dragging it up and down.

This short video shows you how: