Identifying if the player clicked on the upper part of the screen?

Hello, fellow scripters; I made a script(complicated to explain) I was trying to do an experiment or [how would it work] So i did the 'Button1Down' which whenever you click on any part of your screen it would print something. Normally:

local player = game.Players.LocalPlayer
local mouse = player:GetMouse()
repeat wait() until player

function button()
print("Down")
end
mouse.Button1Down:connect(button)

Similar to that: The thing i was willing to find out is [how] From the center of your screen, how will i let my output print 'hi' whenever i click the upper part of the screen instead of clicking "anywhere" on my screen. [Only the upper part; starting from the center]

I would appreciate your help, i can't find the proper term for it and was not able to find any results from google from my own words.