Any window can also be closed by clicking on the close button 
in the upper right corner of the window.
Closes the Structure window.
Any window can also be closed by clicking on the close button in the upper right corner of the window.
To open a Structure window in the Work Area,
Double click on its name in either pane of the Project Panel.
Or right click on its name in either pane of the Project Panel, and execute Open from the menu.