Where are the Portal (Members) files in the Ghost's installation?

I tried to look to look for the portal files on my Ghost installation but couldn’t find it.

On GitHub Portal’s code is available under Ghost organization but on my installation I’m still finding it hard to find where it is?

I’d like to do some customisation with the portal code, please help me find it?

Here https://unpkg.com/@tryghost/portal@0.14.1/umd/portal.min.js
I found it in browser console on Network tab when load ghost page )
See details here https://github.com/TryGhost/Portal#usage

I’m not technical enough to understand that but basically I wanna know where I can find the portal code in my installation, like in our file manager, to customize it. That’s what I’m not able to fiqure out.