@DanCouper thanks. you are right. But my question is why did they chose 60% and 58% at first place is there calculation involved? like we calculated 75em from 1200px.
/* 1200px / 16px = 75em */ @media (max-width: 75em)
It’s arbitrary, could have chosen any unit. Somebody’s eyeballed it as those two numbers being something that they think looks good when applied.
Note that often the root element has a size in px or % set as a base to work from (so 16px or 100%) when you’re doing the CSS for a page, this is the same. What it means is that it changes the font size on the root (<html>) element, so anything else in the CSS that’s sized in ems/rems will derive from that.