How to properly organize a GIT repository(s) for multiple projects with many shared files?

Question

git

There are projects A and B: HTML, JS, CSS.
HTML and JS one to one. The only difference between projects is CSS files + graphic assets.
Development goes on project A. After the delivery of the next version, project B catches up with project A to this version: the corresponding CSS is written, resources are cut. If you have to adjust the HTML to design B, then it is adjusted accordingly in project A to be completely identical. While project B is being developed, development on A does not stop.
Today these are two different repositories. Every time project B has to do a merge for HTML, JS (actually also LESS and a lot of other common things), etc. Project C is on the way, which will work on the same principle.
I would like to organize this whole thing so that HTML, JS would be only in a single instance, and commits to project B can be seen separately / outside project A. Working in project B, of course, you need to see the HTML, JS of project A.
I looked towards git-submodule, but I don't understand how it can help me.

Answer 1

How to organize version control of two identical sites?