CSS - the presentational layer

Cascading Style Sheets (CSS) is a W3C standard for defining the presentation of web documents

We will define "presentation" as meaning the visual aspects of how a web document is displayed on a computer monitor. If you create a web page, it will display as you instructed it to display, even if you inadvertently instructed it to display as someone else instructed it.

To be a bit more clear,

each html tag has to display in some fashion and a browser looks for instructions telling it how to display the tag. If it finds none, it will display the element according to the browser's own display rules

For example, this page shows how several basic tags display when the page provides no specific instructions telling it what to do. In this case, the browser defaults to its own set of display rules.

Here is the same page using a set of display rules created by the page author and here is the same page using a set of display rules created by another individual. Toggle back and forth to see the difference.

These display rules can be applied to one or more pages and then any change made to the rules will apply to all pages linked to the rules.

W3Schools has a similar example.


Benefits of CSS

Greater typography and page layout controls

Greater control over how your type displays; you can be explicit in your definitions

Less work

One edit, multiple simultaneous corrections; really useful in a large site

Potentially smaller documents

You need only create a link to a single list of rules, rather than recreate the rules in each page you create.

Let's go back and look at our MSWord-created page for a comparison. It has all the display rules for all the possible tags embedded in the page file.

Potentially more accessible documents

Though it is easier to control the placing of objects on a web page using visual tools such as tables, such tables are not always useful for all users.

CSS guidelines allow you to build pages that are accessible by a far wider span of potential users.

Presentational HTML is on its way out

Mixing the rules about what an object means and how it should look on a single page is a thing of the past.

Even though current browsers still support such activities, eventually they will drop this ability and all pages will need to conform to the CSS standard

You will follow CSS rules for your task 02, so it would be a good idea to get used to them now

CSS is well-supported

Nearly all browsers support most of CSS-1, most also support the majority of the Level 2 and 2.1 recommendations.


CSS - THEORY | in practice | 02.02 | next session