A rule selects the elements in which you want to apply formatting to and then indicates what should be done to them. In order words, a rule is a code statement. It consists of two parts: The selector and the declaration.
* The 'selector' identifies one or more HTML, elements that you want to work with. You commonly select an element by its type.
* The 'declaration' consists of a property and a value that specifies how to format the elements identified by the selector.
selector ( property: value )
h1 ( font-size: 18px; font-weight: bond; )
** You can do many things that are either difficult or impossible when using ordinary HTML.
** CSS is case insensitive, except for the parts that reference specific parts of an HTML document.(p.294)
Cascading refers to the prioritizing that takes place when more than one property declaration applies to the same element in your HTML document. In other words, which style declaration wins out? The winner is based on the following levels of priority, starting with the highest: