Cascading Style Sheets (also known as CSS) allows us to separate presentation from content. This is how we can re-use the same content in different forms. CSS is what lets us apply different styles in different contexts, and CSS is what lets us change the "look and feel" of an entire website with just a few keystrokes. CSS saves a webmaster a lot of work if used properly, and provides a great deal of flexibility in how all the pages of a site are displayed. CSS also provides a great deal of flexibility in reusing content.
The "slides" I have posted online cover the core of how to make CSS code happen. We are going to "walk through" at least the first slide-set in class, so I can be available to answer the questions which inevitably arise from looking at this material. Do not let the mass of details worry you. The basics are actually not very difficult, once you get used to the notation used, and the coding practice you will go through in this class should help a lot.
These are called "cascading" style sheets because you can apply more than one to the same document, and because each additional style sheet applied to a document can add to or over-ride the settings established in previously-applied style sheets. For example, you can have a basic stylesheet which gets applied to all the pages at a website first to establish a site-wide "look and feel", and then an additional stylesheet for each "area" of your website.
Say you have divided the pages at your website into several "chunks": one set of pages about the various products sold at the site, and another set of pages with product support information. You could then apply a second stylesheet specific to all the product pages (say, setting a light yellow background for those pages) and you could apply a different second stylesheet to all the product support pages (say, setting a light orange background for those pages).
What is an example of a situation in which you might want to re-use the same content by applying different styles?