The very first thing you need to know about CSS is that it uses the language of print layout, not programming.
A lot of the problems programmers seem to have with CSS probably stem from this misapprehension.
A lot of the problems programmers seem to have with CSS probably stem from this misapprehension.
I imagine the slash in CSS grid is for similar syntactic reasons, because the syntax also admits hyphenated identifiers [1] (custom-ident), which precludes the use of “-”. (They could have used a range operator like “~” or “..” though.)
[0] https://en.wikipedia.org/wiki/Slash_(punctuation)#Numbering
[1] https://developer.mozilla.org/en-US/docs/Web/CSS/grid-column...