Unity runtime coordinate system is different than while developing ?

Hi ! I am very new to Unity. I am experiencing a weird problem.
I am trying to get coordinates from mouse click. But during runtime the origin seems to be shifting to top-left corner but during developing I had arranged it to be at exact center of my camera. How to get the input in the original coordinate system ?
Any suggestion is greatly appreciated !

Thanking you

Mouse Input treats the bottom left corner of the screen as (0,0).

People use Camera.ScreenToWorldPoint() or Camera.ScreenPointToRay() to convert to world coordinates.