There are two type CSS rule

1. ruleset

2. at-rule.

Ruleset identifies selector or selectors and declares style which is to be attached to that selector or selectors. For example P {text-indent: 10pt} is a CSS rule. CSS rulesets consist of two parts: selector, e.g. P and declaration, e.g. {text-indent: 10pt}. P {text-indent: 10pt} - CSS rule (ruleset) {text-indent: 10pt} - CSS declaration text-indent - CSS property 10pt - CSS value.