What is a 4px bug?

Question

Layout

What does the bug of four pixels in the layout mean?
I heard about him from an interview with IT Beard.
Because of this bug, designers try to make indents in layouts a multiple of 4.
But there is no information in Google about this bug, four pixels.

Answer 1

- Where did the extra pixels in the layout come from?
- Half a pixel?
- 10 CSS Tricks You Might Not Know

Answer 2

4-pixel padding in the design is just convenient and has become a kind of standard. More variability than 5px and even more convenient 10px. Originally came from mobile development.
This grid allows you not to follow the numbers (for example, when you need to indent strictly at least 10px, although visually it asks for less), but at the same time keep the styles in order so that the developer does not go crazy and there is logic in the design.
It has nothing to do with the bug, whatever it is.