View without gridlines and task numbers

Hello - when I started entering tasks there was a simple, clean view. Then I think I must have accidentally pressed a keyboard shortcut perhaps, because the view changed to one with gridlines, task numbers on the right (I assume these refer to the order in which the task was created), and tree-view icons that represent the number of subtasks.

Is there any way to go back to the intial 'clean' view?

Thanks