How to merge two css files?

Question

css

Good afternoon!

Such a situation happened, they gave the first part of the layout to the back, and after that the second part was made ... And the backend changed the css file, and now I need to synchronize them somehow.

That is, there are two css files, they are 99% similar, but they have differences, and I need to merge them somehow ...

The second part of the layout is done in scss, since I am already doing it. But in the course of testing the old layout, I corrected the old css and damn back its rules ... As a result, I don’t know how to synchronize them ((

I don’t understand why back didn’t give me the task, I would fix everything, and in theory if the first part was on scss, I could fix it normally, but not back in the file that was built.But due to the past developer, the first part is on css, so it's a little easier than it could be