Why does the horizontal scroll appear?

Question

css

I beg you to explain why if you start to reduce the screen to about 1200px or less, then a small horizontal scroll appears?
https://codepen.io/anon/pen/KRGywO
I'm using a Flexbox Grid as a grid. So, if margin: 0 is specified for body (which is actually specified in normalize.css by default), then a small scroll appears ... What is the reason for this behavior? Thanks in advance for any help.

Answer 1

https://codepen.io/topicstarter/pen/zjmPNo something you have more width - when specifying max-width, it fell into place, look for what pops out

Answer 2

Removed, the scroll is gone

.row {
  margin-right: -0.5rem;
  margin-left: -0.5rem;
}