How to indent between sections?

Question

HTML

I do not know how to make the distance between the sections, it should be the same everywhere. If I write some margin , then the section goes to the next line, in theory the section should narrow, but this does not happen.
https://codepen.io/roman-zolotov/pen/vYNdXzE

Answer 1

.col-lg-4 {
width: calc(33.33% - 15px);
margin-right: 15px;
}

Answer 2

Well, since I have already begun to take the ideas of the columns from the bootstrap - why don't you continue?
do for .row {margin: 0 -15px;}
and for cols padding: 0 15px;