A controller for controlling the display of secondary digital content displayed in an overlay above a primary video stream. The controller includes a touch interface device, a processor, and a memory storing non-transitory instructions. These instructions, when executed, can include (i) detecting a first input gesture by a user on the touch interface device, (ii) in response to detecting the first input gesture, selecting an application for display, (iii) detecting a second input gesture by the user on the touch interface device, (iv) in response to detecting the second input gesture, scrolling through a currently-displayed layer of the selected application displayed, (v) detecting a third input gesture by the user on the touch interface device, and (vi) in response to detecting the third input gesture, scrolling between layers of the selected application in a simulated Z-space.