Where can I find the grid for the site?

Question

css

So that instead of bootstrap there is only a grid and it is desirable that all classes are written in CSS and not HTML

Answer 1

Take from the same bootstrap (or any other) and build your own on its basis, through trial and error.
This is the most efficient way.

Answer 2

1. Set up the bootstrap in such a way that only the grid would be loaded.
2. Create your grid