What is the best way to design your grid on Grid through classes?

Question

css

Good evening, I need to understand the construction of self-written grids, the choice fell on Grid, but I can’t figure it out completely. Ideally, I want to write something like this - goo.gl/7s74j9 , but in such a way that more blocks can be added to the block. But for starters, at least break how to make a class grid, like in Bootstrap, if there are such craftsmen, I want to call my team, I hope for reasonable answers, thanks in advance!