Simple cross platform style guide for mobile apps or a recommended approach?

Having joined a new project recently I've found a lot of padding / margin sizes etc set in the App which had variuous names and isn't consistent.

I've also been briefly looking at style guides blog posts.

I'm trying to come up with a simple style guide, which will cater font sizes, margins and padding.

However, I'm trying to arrive at something simply which will cater for most scenarios.

I've previously encountered policies based on a number aka 4 or 5 and margins had to be multiples of that. I think that was along the lines of bootstrap.

Can anyone point me at something similar which would work for Android and iOS...