A rule is a statement that tells a browser how to draw a particular element on a web page.
A rule has two parts: a selector and a declaration.
A selector identifies the elements on a web page that are affected by the rule. The declaration tells the browser how to display the element that is selected by the selector.
The preceding post has 4 rules.
There are four selectors: body, h1, p and note.
The declarations for each rule are inside curly braces. Each declaration can contain one or more properties. A semi-colon separates properties.