Since it is a Godot project, the problem probably is somewhere in the Camera2D or Project Setting > Display(Window), if I had to guess.
There is no Camera2D, I think the problem is either in the Project Setting > Display(Window) as you say or in the Export settings, because I changed Project > Export > Web(Runnable) > HTML > Canvas Resize Policy from "Adaptive" to "None".
ah ok, yes this can also be it. i left the default settings for web export.
