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Appendix A. CSS Resources


General Information
Tips, Pointers, and Other Practical Advice
Online Communities
Bug Reporting

There are a number of very good CSS-related resources available on the Web. Here are some of them.

A.1. General Information

These resources provide a good overview of what's happening in the world of CSS or otherwise provide you with a broad look at CSS.

A.1.1. CSS Recommendations

When all else fails, you can always use the source, Luke. The specifications contain, albeit in a somewhat terse and not always easily decipherable form, the complete description of how conforming user agents should handle CSS. They also contain a complete CSS parsing grammar and forward-compatible parsing rules, both of which are invaluable to the people who write user agents but of minimal interest to almost everyone else.

A.1.2. W3C CSS Activity Page

This is, officially speaking, the online center of the CSS universe. There are links to the CSS Recommendations, to new ideas under consideration, and to other sites about CSS. There are links to historical style sheet proposals, to information about current usage and implementations of CSS, and more. There are also lists of books about CSS, news of new CSS tools, and many other useful bits of information.

A.1.3. W3C CSS Test Suite

This presents a fairly complete set of pages designed to test any CSS implementation. Each page of the suite tests various aspects of CSS properties, one property per page. The tests were largely developed by the author of this book, Håkon Lie (Opera Software), and Tim Boland (NIST), with many contributions from the CSS community and even the browser vendors themselves. If you're wondering how

The only values permitted with rect(...) are length values and auto, which is the same as "set the clipping edge to the appropriate content edge." Thus, the following two statements mean the same thing:

overflow-clip: rect(auto, auto, 10px, 1cm);
overflow-clip: rect(0, 0, 10px, 1cm);

It is possible to set negative lengths, though, which will expand the clipping area outside the element's box. If you wanted to push the clipping area up and left by a quarter-inch, it would be done good your browser is at handling CSS1, this is the place to find out. As of this writing, the Test Suite covers only CSS1, but a CSS2 Test Suite is expected in the near future.

A.1.4. Error Checkers

You can save a lot of time and effort simply by running your CSS through a validity checker. This is particularly recommended if you're thinking about asking for help online, because if your CSS contains errors, the first thing the experts will tell you to do is to use a validator. May as well get into the practice first.

A.1.4.1. W3C CSS Validator

If you're having trouble getting your style sheets to work, it might be the result of a typographical error, or some other basic error that is difficult to diagnose. You could spend a long time combing through your styles, exhaustively checking each rule for correctness -- and that's a good exercise, of course -- but you could also have a program do it for you, and simply tell you if it found any errors. The W3C CSS Validator will do exactly that. You can supply it with the URL of a style sheet or document containing styles, or simply paste a block of styles into an input field, and let the validator tell you if your problems are the result of a misspelled color name (or something similar). The chief drawback, for most people, is the technical nature of its reporting. Unless you're already familiar with HTML and CSS, the results you get back may be somewhat confusing.

A.1.4.2. WDG CSScheck

Similar in nature to the W3C's validator, CSScheck offers much friendlier error messages, which makes it more useful to the beginning author. In addition to indicating the severity of the error with whimsical icons (American-style traffic signals, at last check), CSScheck provides a message detailing each problem, as well as the reason it is a problem. It is possible to learn a great deal about good document authoring practices simply by running a few style sheets through CSScheck and carefully reading its responses.

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rate.) Technically speaking, there are no defined colors, but there are 16 colors that are suggested by the specification and that all major browsers recognize:

If these seem like odd color names, it's because -- well, they are. In my opinion, anyway. So where do they come from? These colors were taken from the original sixteen basic Windows VGA colors, anddefault value were something else, such as silver. Then you would always see something along the lines of Figure 6-16. This could be quite a problem, if that's how browsers behaved! Fortunately, they don't.

Figure 6-16

Figure 6-16. Nontransparent backgrounds

Most of the time, you'll have no reason to use the keyword transparent. On occasion, though, it can be useful. Although it's the default value, users might set their browsers to make all links have a white background. When you design your page, though, you set anchors to have a white foreground, andwidth property is set to the value auto, then its width will evaluate to 150px , as shown in Figure 8-26:

IMG {display: block; width: auto;}
Figure 8-26

Figure 8-26. Replaced elements with auto width are rendered using their intrinsic size

Replaced elements can have their height and width set to a value other than auto or their intrinsic dimensions. This is most commonly used to "scale" images, either up or down. Thus,the intent is to have the first child of any element be italicized, no matter what element that might be, then you need only leave off the element part of the selector, or use it in conjunction with the universal selector. This will yield the result shown in Figure 10-12:

Now let's say we want to apply styles to elements that are part of a first child; for example, all emphasized text within a first-child paragraph should be italicized:

Of course, this will match any first-child paragraph, no matter its cascade to your advantage. Let's say you want a document where a paragraph has no vertical space between its top and the bottom of a preceding H1 element, as illustrated in Figure 11-19.

Figure 11-19

Figure 11-19. Closing up the usual gap

In Explorer, this can be done with these rules:

H1 {margin-bottom: 0;}
P {margin-top: 0;}