Here are some places where you can find out more about CSS Syntax, Selectors, Properties and Values.
Mozilla Developers Network: MDN
This site sets the standard as a reference for all things web.
CSS: Cascading Style Sheets
This is the main area for all things CSS at MDN
CSS Syntax
CSS Reference
CSS Tricks
This is an excellent resource not only on CSS but also for front-end web development in general.
CSS Tricks Homepage
CSS Ruleset Terminology
A ruleset is what applies CSS to an element or elements. This is the core syntax for CSS.
