How to scale everything to 125%? (Pantheon)

I am using a laptop, and under Windows, I usually use 125% scale. When I used Arch Linux before, I achieved 125% scale by setting Xft.dpi: 120 in ~/.Xresources.
But under nixos, this method failed. I have tried services.xserver.dpi = 120; but this method is completely invalid.
So, how can I achieve a 125% scale?

This is my configuration.nix.