What is CSS Syntax? w3schools defines it as : a CSS rule-set consists of a selector and a declaration block: The selector points to the HTML element you want to style. The declaration block contains one or more declarations separated by semicolons.
Russ Weakley started the article with the explanation of Backus-Naur Form :
Backus–Naur Form (BNF) is a formal notation used to describe the syntax of computer languages. It is designed to be unambiguous, so that there is no disagreement or ambiguity as to how the language can be expressed.
There are many more explanation on it, head down to the article!