CSS

CSS

CSS (Cascading Style Sheets) is a language used to alter the visual presentation (presentation semantics) of a document written in (X)HTML.  (X)HTML has a default style and look, and with CSS one in in practice alter the look of an (X)HTML element to look like any other.

CSS also has some uses for example for users that cannot see, in that the tool used by users (for example braille machines, machines that text content via a line of pins that move up and down) is instructed to show extra content to users of braille (media="braille") so that they can more easily have an overview of sections of the site, in particular that the navigation box is prepended and appended by navigation start and navigation end headers (headers are used by visually impaired users to jump between different parts of a page).  The same headers are hidden for regular users using CSS.

Without CSS web pages could look a little boring, and there are many examples of wonderful designs using CSS.  Before CSS, a lot of work went into making HTML look good, and many different hacks and (X)HTML element attributes existed to alter the look of web pages.

With CSS, one can now have a clear and tidy separation of content semantics ((X)HTML) and presentation semantics (CSS).  This enables the full semantic range of (X)HTML to be used, while users can get some eyecandy while browsing around on the web and web publishers can do many different things to look good and be attractive.

Javascript has its uses with CSS as well, in that web pages "come alive" with Javascript;  CSS is static, while Javascript can make changes to CSS "values" when the page has been loaded.  For example one can create a big blue box within a web page with a message after a user has pressed on a button in the web page.  This could also have been done using only HTML and CSS, but in this example Javascript enables a rapid and "application-like" response, making a webpage feel more like a native computer application.