CSS rule is a combination of selectors and declarations.
The selector is the HTML element which you want to style.
Each declaration consists of a property and a value.
The property is a style attribute you want to change. Each property has a value.
A CSS declaration must ends with the semicolon,and declaration groups are surrounded by curly brackets:
font-family:Arial, Helvetica, sans-serif;
In the style definition you should define how each selector work (font, color etc.).
Then, in the HTML code of web pages, you can refer to these selectors for activate, the styles.
There are three types of selectors are:HTML (TAG) selectors
Used to define styles associated to HTML tags. (A way to redefine the look of tags)
Used to define styles that can be used without redefining plain HTML tags.
Used to define styles relating to objects with a unique ID (most often layers)
Comments are used for explain your codes, it can be useful for edit the source code later. Comments are ignored by the browsers.
A CSS comment begins with "/*", and ends with "*/", like this:
/*This is a comment*/
/*font-family:Arial, Helvetica, sans-serif;*/