Some advantages of CSS is that CSS defines how the page looks like in a certain place on the webpage without having to write it more than once. It is easier to change because you defined how th id, class, and html tags in the external style sheet, so when the webpage is linked to the external style sheet, whatever tag is defined in the style sheet, it will apply to the page. CSS also makes positioning the content on the page by pixels. The webpage will also load faster because that html file isn't filled with tags that define how the page will look. Instead, it is define in the external style sheet. The only disadvantage is that it doesn't work on browswers lower than version 4.
In CSS, we define styles in an External Style Sheet or just in the html file. An External Style Sheet is a seperate CSS file that is not apart of the file for the webpage. In this style sheet, it redefines HTML tags and defines class and id tags. If you only want a certain little part changed in your webpage, a style sheet can be added to the html document itself to change that little part.
Class selectors are used to define styles that can be used without redefining plain HTML tags. An example is putting a class="nav" in the a href tag. Whatever the nav is defined in the style sheet, it will apply to this link. To define this tag, in the style sheet, there's has to be a part that say:
a.nav:link{define style here} or
a.nav:visited{} or
a.nav:hover{}
ID selectors are used to define styles relating to objects with a unique ID. It is similar to the class tag and used almost the same way but it is just written different in the style sheet. Lets just say we put "id=top" in a tag, in the style sheet, it is defined like this:
#top{}
HTML selectors are used when you want to redefine the general look for an entire HTML tag. Lets say that the 'b' tag is redefine as something else, when 'b' is used in the html file, however it is defined in the style sheet, it will look like how it is defined if the html file is linked to the external style sheet.
Someways that CSS can be used to change how a webpage looks is its positioning, its text, color, links, lists, layers, and cursors. CSS can also define the background picture of a page. For example, you can make the text in arial, red and blue text, white links, no bullets lists, and an arrow for a cursor.