Thursday 19th of January 2017 01:53:41 PM
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
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,
Figure 6-42. Declaring only one percentage means the vertical position evaluates to 50%
Table 6-2 gives a breakdown of keyword and
Table 6-2. Positional Equivalents
In case you were wondering, the default values for
background-position are 0%
0%, which is functionally the same as
top left. That's why,
unless you set different values for the position, background images
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.
0.1. Typographical Conventions
The following typographical conventions are used in this book:
- Constant width
is used to indicate code examples, HTML tags and CSS elements.
- Constant width italic
is used for replaceables that appear in text.
is used to introduce new terms and to indicate URLs, filenames, and
indicates a note or tip relating to the nearby text.
indicates a warning.
Copyright © 2002 O'Reilly & Associates. All rights reserved.
As we can see from Figure 8-22, the paragraph hassimply been pulled upward by its negative top margin, such thatit's outside the parent DIV !
Figure 8-22. The effects of a negative top margin
With a negative bottom margin, though, it looks as though everythingfollowing the paragraph has been pulled upward. Compare the followingmarkup to the situation shown in Figure 8-23: