Why is padding used instead of margin when indenting between columns?

Question

css

There are 3 columns at 33.3% why when you need to indent between columns, they are done using padding? Although it would be more logical with the help of margins. Just not to bother with width calculations? Since box-sizing: border-box; takes into account paddings and borders.

Answer 1

you can also use margins - width: calc((100%/3) - 20px)
jsfiddle.net/weq46z76/1

Answer 2

Including because of box-sizing: border-box. But just, as far as I remember, margin works crookedly with cells. But I may be wrong.