The subject of this book is, as you might have guessed by the cover, Cascading Style Sheets (CSS). There are two "levels" to CSS; these are referred to as CSS1 and CSS2. The difference between the two is that CSS2 is all of CSS1, plus a lot more. This book attempts to cover all of CSS1, and CSS positioning, which is a part of CSS2. The rest of CSS2 is excluded because, at the time of this writing, nobody had implemented most of it. Rather than cover a lot of theoretical territory, we chose to stick to what was currently usable.
If you are a web designer or document author interested in sophisticated page styling, improved accessibility, and saving time and effort, then this book is for you. All you really need before starting the book is a decent knowledge of HTML 4.0. The better you know HTML, of course, the better prepared you'll be. You will need to know very little else in order to follow this book.
It is important to remember something about web standards and books: the former are continually evolving, while the latter are frozen in time (until the next edition comes out, anyway). In the case of HTML and CSS, there are a great many changes afoot even as these words are being written. The recent formalization of XHTML 1.0 as a full W3C Recommendation, for example, is a major milestone in the evolution of the World Wide Web. There are likely to be even more levels to CSS, further extending the ability to style documents; major web browsers are approaching full CSS1 support, and robust CSS2 implementations can be seen lurking on the horizon. This is an exciting time to be a designer, and learning CSS now will give you a leg up on the future.
The following typographical conventions are used in this book:can be affected by its width, of course; the skinnier a paragraphbecomes, for example, the taller it has to be in order to contain allof the textual (and other) content.
In CSS, it is possible to set an explicit height on any block-levelelement. If this is done, the resulting behavior is somewhatuncertain. Assume that the specified height is greater than thatneeded to display the content:
<P STYLE="height: 10em;">
is used to indicate code examples, HTML tags and CSS elements.
is used for replaceables that appear in text.
is used to introduce new terms and to indicate URLs, filenames, and pathnames.
indicates a note or tip relating to the nearby text.
indicates a warning.
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The simplest way to set a margin is by using the property margin.
Percentage values refer to width of the parent element.
Suppose we wish to set a quarter-inch margin on H1 elements, position of the element are defined by a combination of theproperties height, width,top, right,bottom, and left, plus anymargins, padding, and borders set for the element. Absolutelypositioned elements can have margins, but these margins do notcollapse.