Äīźóģåķņąöč˙
HTML CSS PHP PERL äšóćīå

1.2 CSS to the Rescue

 
Previous Page Table of Contents Next Page

1.2 CSS to the Rescue

Of course, the problem of polluting HTML with presentational markup was not lost on the World Wide Web Consortium (W3C), which began searching for a quick solution. In 1995, the consortium started publicizing a work-in-progress called CSS. By 1996, it had become a full Recommendation, with the same weight as HTML itself. Here's why.

1.2.1 Rich Styling

In the first place, CSS allows for much richer document appearances than HTML ever allowed, even at the height of its presentational ferver. CSS lets you set colors on text and in the background of any element; permits the creation of borders around any element, as well as the increase or decrease of the space around them; lets you change the way text is capitalized, decorated (e.g., underlining), spaced, and even whether it is displayed at all; and allows you to accomplish many other effects.

Take, for example, the first (and main) heading on a page, which is usually the title of the page itself. The proper markup is:

<h1>Leaping Above The Water</h1>

Now, suppose you want this title to be dark red, use a certain font, be italicized and underlined, and have a yellow background. To do all of that with HTML, you'd have to put the h1 into a table and load it up with a ton of other elements like font and U. With CSS, all you need is one rule:

h1 {color: maroon; font: italic 2em Times, serif; text-decoration: underline; 

      background: yellow;}

That's it. As you can see, everything you did in HTML can be done in CSS. There's no need to confine yourself to only those things HTML can do, however:

h1 {color: maroon; font: italic 2em Times, serif; text-decoration: underline; 

      background: yellow url(titlebg.png) repeat-x; 

      border: 1px solid red; margin-bottom: 0; padding: 5px;}

You now have an image in the background of the h1 that is only repeated horizontally, and a border around it, which is separated from the text by at least five pixels. You've also removed the margin (blank space) from the bottom of the element. These are feats that HTML can't even come close to matching—and that's just a taste of what CSS can do.

1.2.2 Ease of Use

If the depth of CSS doesn't convince you, then perhaps this will: style sheets can drastically reduce a web author's workload.

First, style sheets centralize the commands for certain visual effects in one handy place, instead of scattering them throughout the document. As an example, let's say you want all of the h2 headings in a document to be purple. Using HTML, the way to do this would be to put a font tag in every heading, like so:

<h2><font color="purple">This is purple!</font></h2>

This has to be done for every heading of level two. If you have 40 headings in your document, you have to insert 40 font elements throughout, one for each heading! That's a lot of work for one little effect.

Let's assume that you've gone ahead and put in all those font elements. You're done, you're happy—and then you decide (or your boss decides for you) that those h2 headings should really be dark green, not purple. Now you have to go back and fix every single one of those font elements. Sure, you might be able to find-and-replace, as long as headings are the only purple text in your document. If you've put other purple font elements in your document, then you can't find-and-replace because you'd affect those too.

It would be much better to have a single rule instead:

h2 {color: purple;}

Not only is this faster to type, but it's easier to change. If you do switch from purple to dark green, all you have to change is that one rule.

Let's go back to the highly styled h1 element from the previous section:

h1 {color: maroon; font: italic 2em Times, serif; text-decoration: underline; 

      background: yellow;}

This may look like it's worse to write than using HTML, but consider a case where you have a page with about a dozen h2 elements that should look the same as the h1. How much markup will be required for those 12 h2 elements? A lot. On the other hand, with CSS, all you need to do is this:

h1, h2 {color: maroon; font: italic 2em Times, serif; text-decoration: underline; 

          background: yellow;}

Now the styles apply to both h1 and h2 elements, with just three extra keystrokes.

If you want to change the way h1 and h2 elements look, the advantages of CSS become even more striking. Consider how long it would take to change the HTML markup for an h1 and 12 h2 elements, compared to changing the previous styles to this:

h1, h2 {color: navy; font: bold 2em Helvetica, sans-serif;

          text-decoration: underline overline; background: silver;}

If the two approaches were timed on a stopwatch, I'm betting the CSS-savvy author would handily beat the HTML jockey.

In addition, most CSS rules are collected into one location in the document. It is possible to scatter them throughout the document by grouping them into associated styles or individual elements, but it's usually far more efficient to place all of your styles into a single style sheet. This lets you create (or change) the appearance of an entire document in one place.

1.2.3 Using Your Styles on Multiple Pages

But wait—there's more! Not only can you centralize all of the style information for a page in one place, but you can also create a style sheet that can then be applied to multiple pages. This is done by a process in which a style sheet is saved to its own document and then imported by any page for use with that document. Using this capability, you can quickly create a consistent look for an entire web site. All you have to do is link the single style sheet to all of the documents on your web site. Then, if you ever want to change the look of your site's pages, you need only edit a single file and the change will be propagated throughout the entire server—automatically!

Consider a site where all of the headings are gray on a white background. They get this color from a style sheet that says:

h1, h2, h3, h4, h5, h6 {color: gray; background: white;}

Now let's say this site has 700 pages, each of which uses the style sheet that says the headings should be gray. At some point, it's decided that the headings should be white on a gray background. So the site's webmaster edits the style sheet to say:

h1, h2, h3, h4, h5, h6 {color: white; background: gray;}

Then she saves the style sheet to disk and the change is made. That sure beats having to edit 700 pages to enclose every heading in a table and a font tag, doesn't it?

1.2.4 Cascading

That's not all! CSS also makes provisions for conflicting rules; these provisions are collectively referred to as the cascade. For instance, take the previous scenario in which you import a single style sheet into several web pages. Now inject a set of pages that share many of the same styles, but also include specialized rules that apply only to them. You can create another style sheet that is imported into those pages, in addition to the already existing style sheet, or you could just place the special styles into the pages that need them.

For example, on one page out of the 700, you might want headings to be yellow on dark blue instead of white on gray. In that single document, then, you could insert this rule:

h1, h2, h3, h4, h5, h6 {color: yellow; background: blue;}

Thanks to the cascade, this rule will override the imported rule for white-on-gray headings. By understanding the cascade rules and using them to your advantage, you can create highly sophisticated sheets that can be changed easily and come together to give your pages a professional look.

The power of the cascade is not confined to the author. Web surfers (or readers) can, in some browsers, create their own style sheets (called reader style sheets , obviously enough) that will cascade with the author's styles as well as the styles used by the browser. Thus, a reader who is colorblind could create a style that makes hyperlinks stand out:

a:link, a:visited {color: white; background: black;}

A reader style sheet can contain almost anything: a directive to make text large enough to read if the user has impaired vision, rules to remove images for faster reading and browsing, and even styles to place the user's favorite picture in the background of every document. (This isn't recommended, of course, but it is possible.) This lets readers customize their web experience without having to turn off all of the author's styles.

Between importing, cascading, and its variety of effects, CSS is a wonderful tool for any author or reader.

1.2.5 Compact File Size

Besides the visual power of CSS and its ability to empower both author and reader, there is something else about it that your readers will like. It can help keep document sizes as small as possible, thereby speeding download times. How? As I've mentioned, a lot of pages have used tables and font elements to achieve nifty visual effects. Unfortunately, both of these methods create additional HTML markup that drives up the file sizes. By grouping visual style information into central areas and representing those rules using a fairly compact syntax, you can remove the font elements and other bits of the usual tag soup. Thus, CSS can keep your load times low and your reader satisfaction high.

1.2.6 Preparing for the Future

HTML, as I pointed out earlier, is a structural language, while CSS is its complement: a stylistic language. Recognizing this, the W3C, the body that debates and approves standards for the Web, is beginning to remove stylistic elements from HTML. The reasoning for this move is that style sheets can be used to create the effects that certain HTML elements now provide, so who needs them?

Thus, the XHTML specification has a number of elements that are deprecated—that is, they are in the process of being phased out of the language altogether. Eventually, they will be marked as obsolete, which means that browsers will be neither required nor encouraged to support them. Among the deprecated elements are <font>, <basefont>, <u>, <strike>, <s>, and <center>. With the advent of style sheets, none of these elements are necessary. And there may be more elements deprecated as time goes by.

As if that weren't enough, there is the very strong possibility that HTML will be gradually replaced by the Extensible Markup Language (XML). XML is much more complicated than HTML, but it is also far more powerful and flexible. Despite this, XML does not provide any way to declare style elements such as <i> or <center>. Instead, it is quite probable that XML documents will rely on style sheets to determine the appearance of documents. While the style sheets used with XML may not be CSS, they will probably be whatever follows CSS and very closely resembles it. Therefore, learning CSS now gives authors a big advantage when the time comes to make the jump to an XML-based Web.

So, to get started, it's very important to understand how CSS and document structures relate to each other. It's possible to use CSS to affect document presentation in a very profound way, but there are also limits to what you can do. Let's start by exploring some basic terminology.

    Previous Page Table of Contents Next Page
    © 2000- NIV