Figure 13.4 shows the results of linking this style sheet to the HTML file from Listing 13.1 FIGURE 13.4 Positioning proper-ties define the rough outline of the page.. Listing 13.3 is a
Trang 1So what’s happening here?
n The first rule sets the margin and padding of the <body>to0 This is an important
first rule for layout because browsers typically add one or the other (or both) to any
web page
n The#sitenavrules in Listing 13.2 are used to turn the ordered list of links into a
horizontal navigation bar
n The#mainsection is set to position: relativeto become the containing block
around the #content,#sidebar, and #footersections
n The#mainsection is also given a large padding on the right, 12em This is where
the#sidebarwill be located
n Absolute positioning is used to move the #sidebarinto the margin, out of its place
in the normal flow of content It is positioned 1 em to the left of the right edge of
its containing block (#main) by right: 1em, and 1 em down from the top edge of
the containing block by top: 1em
Figure 13.4 shows the results of linking this style sheet to the HTML file from Listing 13.1
FIGURE 13.4
Positioning
proper-ties define the
rough outline of
the page.
It’s still quite rough, but you can see the different sections moved into place You should
note the silver bars above and below the header Where did they come from, and why?
Trang 2The silver bars are the result of the background color set on the <body>showing through
They are formed because of the default margin properties set on the <h1>and<h3>
head-ings used on the page Remember that margins are outside of the border of an element’s
box, and the background-colorproperty on a box colors only the interior content, not
the margin This applies even when you have a <div>wrapped around a heading, such as
<h1> The margin extends beyond the edge of the <div>’s background-color
To fix this, we explicitly set the heading margins to zero on the heading tags Listing
13.3 is a style sheet that not only does that, but also assigns colors, fonts, and other styles
on the site The teal, purple, white, and yellow colors were chosen to reflect not only the
original design of the website, but also the actual colors used at the Dunbar school
audi-torium, too
LISTING 13.3 A Style Sheet for Colors and Fonts
/* dunbar-colors-13.3.css */
body { font-family: Optima, sans-serif; }
a:link { color: #055; }
a:visited { color: #404; }
#header { text-align: center;
color: white; background-color: #055; }
#header h1, #header h2
{ margin: 0; }
#header h1 { color: #FFFF00; font-size: 250%; }
#header h2 { font-weight: normal; font-style: italic; }
#sitenav { color: white; background-color: #404; }
#sitenav ol { font-size: 90%; text-align: center; }
#sitenav li { margin-left: 1em;
border-left: 1px solid #DD0; }
#sitenav li a:link, #sitenav li a:visited
{ color: white; text-decoration: none; }
#sitenav li a:hover
{ color: #DDDD00; }
#main { background-color: #055; }
#content { background-color: white; padding: 1em 5em; }
#content h3 { margin-top: 0; }
#content p { font-size: 90%; line-height: 1.4; }
#sidebar h3 { font-size: 100%; color: white; margin: 0;
font-weight: normal; padding: 0.125em 0.25em;
background-color: #404; }
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Trang 3LISTING 13.3 Continued
#sidebar ol { background-color: white; border: 2px solid #404;
border-top: 0; margin: 0 0 1em 0;
padding: 0.125em 0.25em; }
#sidebar li { font-size: 85%;
display: block; padding: 0.125em 0; }
#sidebar li a:link, #sidebar li a:visited
{ text-decoration: none; color: #055; }
#sidebar li a:hover { color: #404; }
#footer { background-color: #404; color: white;
padding: 0.5em 5em; }
#footer p { margin: 0em; font-size: 85%; }
#footer p a:link, #footer p a:visited
{ color: #DDDD00; }
Figure 13.5 shows the HTML file from Listing 13.1 with both the layout style sheet from
Listing 13.2 and the colors and fonts style sheet from Listing 13.3
FIGURE 13.5
Fonts and colors
help define the
website’s look.
As you can see, the styled page in Figure 13.5 looks quite different from the unstyled
version in Figure 13.3
Reordering Sections with Positioning Styles
The page in Figure 13.5 looks okay, but let’s say that you got this far into the web design
Trang 4You could go in and change your HTML source around This would work, but it would
introduce a problem The order of the HTML in Listing 13.1 is sensible—the name of
the site is given first, and then the navigation menu This is how users of non-CSS
browsers such as Lynx will read your page, and also how search engines and screen
read-ers will undread-erstand it as well Moving the title of the page after the list of links doesn’t
make much sense
Instead, you can use CSS positioning properties to reformat the page without touching
the HTML file Listing 13.4 is a style sheet to do exactly that
LISTING 13.4 Moving One Section Before Another
/* dunbar-move-13.4.css */
#header { padding: 1.25em 0 0.25em 0;
position: relative;
background-color: #404; }
#sitenav { position: absolute;
top: 0; right: 0;
border-bottom: 1px solid #DDDD00;
width: 100%;
background-color: #055; }
What’s happening here?
n The#headersection encloses the #sitenavin the HTML source, so by setting it to
position: relative, it now becomes the containing block for the site navigation
links
n Padding is added to the top of the #headersection This is where subsequent rules
will place the site navigation menu; the padding reserves the space for it
n Absolute positioning properties align the top-right corner of the #sitenavsection
with the top-right corner of its containing block, the #header
n Giving a widthof100%to the #sitenavensures it will reach across the full width
of its containing block, which is, in this case, as wide as the browser display
win-dow
n Finally, colors are swapped on the #headerand the #sitenavto make them fit in
better with the overall design in their new locations, and a yellow border is added
to the bottom of the navigation links
Figure 13.6 shows the effects of these changes
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Trang 5▼
FIGURE 13.6
The navigation
menu is now
above the page
headline.
Task: Exercise 13.1: Redesign the Layout of a Page
You just learned how to move the site navigation menu around What if you want to
make further changes to the page? Try these steps to get familiar with how easy it is to
change the layout with CSS:
1 Download a copy of the source code for editing The file dunbar.htmlcontains the
complete HTML page, and dunbar-full.csshas all the style rules listed in this
chapter combined into a single style sheet
2 Move the sidebar to the left side of the page instead of the right To do this, you
need to make space for it in the left gutter by changing the padding rule on the
#mainsection to
#main { padding: 0 2em 2em 12em; }
3 Then change the positioning offset properties the #sidebar You don’t even have to
change the rule for the topproperty; just replace the property name rightwith
left
4 Reload the page You should now see the menu bar on the left side of the screen
5 Next, move the #footersection Even though the id of the <div>is“footer”,
there’s nothing magical about that name that means it needs to be at the bottom of
the page Place it on the right side, where the sidebar used to be located First clear
some space:
Trang 66 Then reposition the footer with these rules:
#footer { position: absolute;
top: 1em; right: 1em;
width: 10em;
padding: 0; }
#footer p { padding: 0.5em; }
7 Reload the page The #footeris now no longer a footer, but a third column on the
right side of the page
The Floated Columns Layout Technique
You can also lay out a web page by using the floatproperty rather than positioning
properties This method is a little bit more complex but is favored by some designers
who prefer the versatility In addition, floated columns can be written with fewer <div>
tags and in some cases deal better with side columns that are shorter than the main text
Listing 13.5 is a style sheet demonstrating how you can float entire columns on a
page with CSS This is a replacement for the dunbar-layout-13.2.cssstyle sheet in
Listing 13.2 The new style sheet places the menu bar on the left instead of the right,
just for variety’s sake—there’s nothing inherently left-biased about floated columns (or
right-biased about positioning)
LISTING 13.5 Float-Based Layouts in CSS
/* dunbar-float-13.5.css */
body { margin: 0; padding: 0; }
#sitenav ol { padding: 0; margin: 0;
display: inline; }
#sitenav li { display: inline; padding-left: 1em;
margin-left: 1em; border-left: 1px
solid black; }
#sitenav li:first-child
{ padding-left: 0; border-left: none;
margin-left: 0; }
/* This is what positions the sidebar: */
#main { padding: 0 2em 2em 12em; }
#content { float: left; }
#sidebar { float: left; width: 10em;
position: relative;
right: 11em; top: 1em;
margin-left: -100%; }
#sidebar ol { margin: 0 0 1em 0; }
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Trang 7What does this style sheet do?
n The first section just duplicates the site navigation bar code from Listing 13.2 so
that the entire style sheet can be replaced by this one
n Starting at the second comment, the code for positioning the columns appears The
first rule sets the #mainsection to have a wide gutter on the left, which is where we
will be placing the sidebar
n Both the #contentand#sidebarsections are set to float This means that they line
up on the left side of the #mainsection, just inside the padding
n A width is given to the #sidebarof10em.The size was chosen because that allows
1 em of space around it, after it is placed inside the 12 em gutter set by the
paddingrule on #main
n A negative margin is set on the left side of the #sidebar, which actually makes it
overlay the #contentsection Relative positioning is then used, via the rightand
toprules, to push the sidebar into the correct place in the gutter
Figure 13.7 shows this style sheet applied to the HTML file in Listing 13.1, along with
the colors and fonts style sheet in Listing 13.3 and the style sheet from Listing 13.4,
which relocated the site navigation menu
FIGURE 13.7
The sidebar is
positioned as
floating content.
Trang 8The Role of CSS in Web Design
As a web developer, skilled in HTML, CSS, and possibly other web languages and
tech-nologies, you have a web development process Even if you haven’t planned it out
for-mally, you’ve got a method that works for you, whether it’s as simple as sitting down and
designing whatever strikes your fancy or as complex as working in a multideveloper
cor-porate development system for a large employer
Adding CSS to your repertoire has made you an even better web developer than before;
your skill set has expanded and the types of designs you can create are nearly limitless
The next step is to integrate your CSS skills into your web development process I’m not
going to tell you exactly how you’ll do that—people have their own methods—but I’ll
help you think about how you can go about using CSS in your web designs
In a few cases, you might develop your style sheets completely separately from your
HTML pages More commonly, you’ll use an iterative process, where you make changes
to the style sheet, then changes to the HTML page, and then go back to the style sheet
for a few more tweaks until you’re satisfied with the results The adaptive nature of style
sheets makes it easy to create these kinds of changes, and you may find yourself
continu-ing to perfect your styles even after you post your content on the Web
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You might not be starting with a blank slate and an uncreated website when you begin using CSS Redesigns are common in web development, and you may want to take advantage of a new site design to convert to a CSS-based presentation It can some-times be harder, but it’s certainly possible to keep the same look and feel of your site when converting it to use CSS If you’re using
a content management system (CMS) that automatically gener-ates your website from a database, converting to style sheets may
be a snap CSS is very compatible, on a conceptual level, with the idea of templates as used by content management systems.
As mentioned at the start of this lesson, CSS design involves balancing a number of
fac-tors to arrive at the best compromise for your site and its users Questions will arise as
you work with CSS on any site, and you’ll need to answer them before you go on Here
are several of these key questions to help you plan your site:
NOTE
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Trang 9n Will you use Cascading Style Sheets, and if so, to what effect? You certainly
aren’t required to use CSS, even after reading this entire book You can create
web-sites that are usable, accessible, attractive, and effective without a single CSS
prop-erty anywhere in evidence However, using CSS will make your site more flexible
and easier to maintain and will give you access to presentation effects you couldn’t
get through HTML alone
n What “flavor” of HTML will you use? HTML5 has a lot of exciting new
fea-tures, but if you’re concerned about older browsers that don’t yet understand
HTML5, you may want to stick with XHTML
n Which browsers will you support? By “support,” I mean investing the effort to
work around the quirks of certain older browsers There are a number of
workarounds for these temperamental browsers, plus ways to exclude certain
browsers from viewing styles But if you are designing just for CSS-enabled
browsers, such as recent Firefox, Safari, or Opera versions, those workarounds
become less important
n Are you using positioning CSS for layout? It’s relatively easy to use CSS for
for-matting text, controlling fonts, and setting colors Using it for layout is trickier,
especially with inconsistent browser support among some of the older versions
n Will you use embedded or linked style sheets? Here, I’ll give you advice: Use
linked style sheets whenever you can Some of the examples in this book may use
embedded style sheets, but that’s mainly because it’s easier to give you one listing
than two
The preceding list isn’t exhaustive; you’ll encounter more choices to make when
design-ing and usdesign-ing CSS, but you should have learned enough by now to answer them
Style Sheet Organization
The way you organize your style sheet can affect how easy it is for you to use and
main-tain your CSS, even if the effects are not evident in the presentation This becomes even
more critical if you’re in a situation where someone else may have to use your styles in
the future You may work with an organization where multiple people will be working on
the same site, or perhaps when you move on to another job your successor will inherit
your style sheets
To make a great style sheet, be organized and clear in what you’re doing, and above all,
use comments Web developers often overlook comments in CSS, but if you have to
come back later and try to figure out why you did something, they’re invaluable
Comments can also be used to group related styles together into sections
Trang 10Reasonable names for classandidattributes can make your style sheet easier to read;
choose names for these important selectors that reflect the functions of the elements If
you can, avoid selectors based solely on appearance characteristics, such as the boldtext
orredboxclasses Instead, try something descriptive of why you’ve chosen those styles,
such as definitionorsidebar That way, if you change your page styles later, you
won’t have to rewrite your HTML There are few things as confusing as a rule like the
following:
.redbox { color: blue; background-color: white; }
In what way is that box red? Well, it probably was red in some prior incarnation of the
style rules, but not now
When you list your rules in your style sheet, do them in a sensible order Generally
speaking, it’s best to start with the body rules first and then proceed down from there, but
because the cascade order matters only in case of conflict, it’s not strictly necessary to
mirror the page hierarchy What’s more important is that you locate the rules that apply
to a given selector and to discern which styles should be applied
An example of bad style sheet organization is shown in Listing 13.6 This is part of the
style sheet from a high-quality website, but with the rules in a scrambled order How
hard is it for you to figure out what is going on here?
LISTING 13.6 A Randomly Organized Style Sheet
#sidebar0 section, #sidebar1 section { font-size: smaller;
border: 0px solid lime; text-transform: lowercase;
margin-bottom: 1em; }
gnav a:link, #nav a:visited, #footer a:link, #footer
a:visited { text-decoration: none; color: #CCCCCC; }
#nav section, #nav shead, #nav sitem, #nav h1 { display:
inline; }
#sidebar1 { position: absolute; right: 2em; top: 3em;
width: 9em; } a:link { color: #DD8800; text-decoration: none; }
#main { } a:hover { color: lime; }
#nav shead, #nav sitem { padding-left: 1em; padding-right:
1em; }
#nav { position: fixed; top: 0px; left: 0px; padding-top:
3px; padding-bottom: 3px; background-color: #333333; color:
white; width: 100%; text-align: center; text-transform:
lowercase; }
#nav section { font-size: 90%; } #layout { padding: 1em; }
body { background-color: white; color: #333333; font-family:
Verdana, sans-serif; margin: 0; padding: 0; }
#nav h1 { font-size: 1em; background-color: #333333; color:
white; } a:visited { color: #CC8866; text-decoration: none; }
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