The basic blocks of CSS are properties and values. Properties are a human-readable identifiers that describe what is being styled. Values indicate how to style that property. When these are paired together they create a CSS declaration
/* Property: color, value: red - together they form a CSS declaration */
CSS declarations are found within CSS declaration blocks. When CSS declaration blocks are paired with selectors (or a list of selectors) they produce CSS rulesets (or CSS rules).
/* p is a selector which together with the CSS declaration block creates a CSS rule */
/* Multiple declarations form a CSS declaration block */