The close button is a shortcut to the close option in the context menu of each item, which
you can open by right-clicking the respective tab. Alternatively to using the mouse, the
context menu can be accessed by pressing the space bar when the desired tab has the
focus (use the tab key to move the focus). Context menus with more options are indicated
by the ". . . " button left to the close button. You can click this button to access the context
menu, containing these options: