rule structure definition

Rule structure is the correct syntax of how to apply styles to HTML and XHTML with CSS. Each rule contains two distinct parts; these parts include the selector and the declaration block.  p {color:black; font-family:serif;} is an example of the rule structure.  P is called the selector.  The other items are part of the declaration block.  Color is the property and black is the value of that property.  And font-family is the property and serif is the value of that property.