Add '+' and '-' icon for zoom in and zoom out

Is it possible to add ‘+’ and ‘-’ while creating map for zoom-in and zoom-out response along with touch or mouse response?
Is it possible to override CSS of infobox?

you can use the camera api to achive this -
create two html buttons (you can use absolute positioning to place them above the maps div).
create an event listener for each button and use viewer.camera.zoomIn() and viewer.camera.zoomOut()

you can also use the viewer.camera.defaultZoomAmount to adjust the amount of zoom in each call