Is it possible to layout the layout with a bootstrap grid, but use separate flexes in css?

Question

css

A question for a million - I make up a layout, I use a bootstrap grid (mainly because of a convenient adaptive), and a question arose if I use a bootstrap grid, but do not use the classes built into 4 bootstrap (like justify-content-center and so on, but I use flexes are already inside css - is this considered stupid practice and shit code? Bootstrap 4 is built on flexes, but let's say in this picture below that I posted, it's easier for me to write the block in col-3 - display: flex, and all its children (div img) write margin: auto so that they would be positioned in the center of the vertical\horizontal, rather than prescribe 3-4 classes in the bootstrap html grid. Is this a normal practice? or will they throw poop? Like
if you typeset on bootstrap 4, then only it.
Or use full flex without grids

Answer 1

CSS Smart Grid was invented especially for you, but you need to know SASS [SCSS] there

Answer 2

.row->.col-3->div style="displat: flex;"->img