CSS: Introduction

Chapter 3

CSS 1: Introduction

Randy Connolly and Ricardo Hoar

Fundamentals of Web Development
Textbook by Prentice Hall
Textbook to be published by Pearson Ed in early 2014
Fundamentals of http://www.funwebdev.com
Web Development
http://www.funwebdev.com

Objectives

1

What is CSS?

2

CSS Syntax

3

Location of Styles
y

4

Selectors

5

The Cascade: How
Styles Interact

6

The Box Model

7

CSS Text Styling



Section 1 of 7

WHAT IS CSS?


What is CSS?
You be styling soon

CSS is a W3C standard for describing the presentation
g
p
(or appearance) of HTML elements.
With CSS, we can assign
• font properties,
• colors,
• sizes,
• borders,
• background images,
p
• even the position of elements.


What is CSS?
You be styling soon

CSS is a language in that it has its own syntax rules.
g g
y
CSS can be added directly to any HTML element (via
the style attribute), within the <head> element, or,
most commonly, in a separate text file that contains
only CSS.



Benefits of CSS
Why using CSS is a better way of describing presentation than HTML

•

The degree of formatting control in CSS is significantly
g
g
g
y
better than that provided in HTML.

•

Web sites become significantly more maintainable
because all formatting can be centralized into one, or a
beca se all formatting can be centrali ed into one or a
small handful, of CSS files.

•

CSS‐driven sites are more accessible.

•

A site built using a centralized set of CSS files for all
presentation will also be quicker to download because
each individual HTML file will contain less markup.
each individual HTML file will contain less markup

•

CSS can be used to adopt a page for different output
mediums.



CSS Versions
Let s
Let’s just say there’s more than 1
there s

•

W3C published the CSS Level 1 Recommendation in
p
1996.

•

A year later, the CSS Level 2 Recommendation (also
more succinctly labeled simply as CSS2) was published.
more s ccinctl labeled simpl as CSS2) as p blished

•

Even though work began over a decade ago, an updated
version of the Level 2 Recommendation, CSS2.1, did not
become an official W3C Recommendation until June
2011.

•

And to complicate matters even more, all through the
And to complicate matters even more all through the
last decade (and to the present day as well), during the
same time the CSS2.1 standard was being worked on, a
different group at the W3C was working on a CSS3 draft.
different group at the W3C was working on a CSS3 draft



Browser Adoption
Insert obligatory snide comment about Internet Explorer 6 here

While Microsoft’s Internet Explorer was an early
p
y
champion of CSS, its later versions (especially IE5, IE6,
and IE7) for Windows had uneven support for certain
parts of CSS2.
parts of CSS2.
In fact, all browsers have left certain parts of the CSS2
Recommendation unimplemented.
CSS has a reputation for being a somewhat frustrating
language.
• this reputation is well deserved!



Section 2 of 7

CSS SYNTAX


CSS Syntax
Rules, properties, values
Rules properties values, declarations

A CSS document consists of one or more style rules.
y
A rule consists of a selector that identifies the HTML
element or elements that will be affected, followed by
a series of property and value pairs (each pair is also
called a declaration).
declaration
selector { property: value; property2: value2; }

rule

syntax

declaration block

selector
em { color: red; }
property

value

examples

p {
margin: 5px 0 10px 0;
font-weight:
font weight: bold;
font-family: Arial, Helvetica, sans-serif;
}



Declaration Blocks
The series of declarations is also called the
declaration block.
• A declaration block can be together on a
single line, or spread across multiple lines.
• The browser
declaration
ignores white space
ignores white space selector { property: value; property2: value2; }
• Each declaration is
declaration block
terminated with a
selector
semicolon.
semicolon.

rule

syntax

em { color: red; }
property

value

examples

p {
font-weight:
font weight: bold;
}



Selectors
Which elements

Every CSS rule begins with a selector.
y
g
The selector identifies which element or elements in
the HTML document will be affected by the
declarations in the rule.
Another way of
thinking of selectors is
thi ki
f l t i
that they are a
pattern which is used
by the browser to
b h b
select the HTML
elements that will
receive the style.

declaration

selector { property: value; property2: value2; }

rule

syntax

declaration block

selector
em { color: red; }
property

value

examples

p {
font-weight:
font weight: bold;
}


Properties
Which style properties of the selected elements

Each individual CSS declaration must contain a
property.
These property names are predefined by the CSS
standard.
declaration
The CSS2.1 Recommendation
defines over a hundred selector { property: value; property2: value2; }
d fi
h d d
declaration block
different property names.

rule

syntax

selector
em { color: red; }
property

value

examples

p {
font-weight:
font weight: bold;
}



Properties
Common CSS properties
Property Type

Property

Fonts

font
font‐family
font‐size
font‐style
font style
font‐weight
@font‐face
letter‐spacing
line‐height
text align
text‐align
text‐decoration
text‐indent
background
background‐color
background‐image
g
g
background‐position
background‐repeat
color
border
border‐color
border‐width
border‐style
border‐top
border‐top‐color
border‐top‐width
etc

Text

Color and background

Borders



Properties
Common CSS properties continued
continued.
Property Type

Property

Spacing

padding
padding‐bottom, padding‐left, padding‐right, padding‐top
margin
margin‐bottom, margin‐left, margin‐right, margin‐top
height
max‐height
max‐width
g
min‐height
min‐width
width
bottom, left, right, top
clear
display
float
overflow
position
visibility
z‐index
list‐style
list‐style‐image
list‐style‐type

Sizing

Layout

Lists



Values
What style value for the properties

Each CSS declaration also contains a value for a
property.
•The unit of any given value is dependent upon
the property.
•Some property values are from a predefined list
of keywords.
fk
d
•Others are values such as length measurements,
percentages, numbers without units, color values,
percentages numbers without units color values
and URLs.



Color Values
CSS supports a variety of different ways of describing color
Method

Description

Example

Name

Use one of 17 standard color names. CSS3
has 140 standard names.
Uses three different numbers between 0
and 255 to describe the Red, Green, and
Blue values for the color.
Uses a six‐digit hexadecimal number to
describe the red, green, and blue value of
the color; each of the three RGB values is
between 0 and FF (which is 255 in
decimal). Notice that the hexadecimal
number is preceded by a hash or pound
symbol (#).
Allows you to add an alpha, or
transparency, value. This allows a
background color or image to “show
through” the color. Transparency is a value
between 0.0 (fully transparent) and 1.0
(fully opaque).
Allows you to specify a color using Hue
Saturation and Light values. This is
available only in CSS3. HSLA is also
il bl
l i SS3 S i l
available as well.

color: red;
color: hotpink; /* CSS3 only */
color: rgb(255,0,0);
color: rgb(255,105,180);

RGB

Hexadecimal

RGBa

HSL


color: #FF0000;
color: #FF69B4;

color: rgb(255,0,0, 0.5);

color: hsl(0,100%,100%);
color: hsl(330,59%,100%);


Units of Measurement
There are multiple ways of specifying a unit of measurement in CSS

Some of these are relative units, in that they are
,
y
based on the value of something else, such as the size
of a parent element.
Others are absolute units, in that they have a real‐
world size.
Unless you are defining a style sheet for printing, it is
U l
d fi i
t l h tf
i ti it i
recommended to avoid using absolute units.
Pixels are perhaps the one popular exception (though
p
p
p p
p
(
g
as we shall see later there are also good reasons for
avoiding the pixel unit).



Relative Units
Unit

Description

px

Pixel. In CSS2 this is a relative measure, while in CSS3 it is Relative (CSS2)
( /
)
absolute (1/96 of an inch).
Absolute (CSS3)

em

Equal to the computed value of the font‐size property of Relative
the element on which it is used. When used for font sizes,
the em unit is in relation to the font size of the parent.

%

A measure that is always relative to another value. The
precise meaning of % varies depending upon which
property it is being used.

Relative

ex

A rarely used relative measure that expresses size in
relation to the x height of an element s font.
relation to the x‐height of an element’s font
Another rarely used relative measure; this one expresses
size in relation to the width of the zero ("0") character of
an element’s font.

Relative

,
Stands for root em, which is the font size of the root
element. Unlike em, which may be different for each
element, the rem is constant throughout the document.

Relative

ch

rem

vw, vh

Type

Stands for viewport width and viewport height. Both are
percentage values (between 0 and 100) of the viewport
(browser window). This allows an item to change size
(browser window) This allows an item to change size
when the viewport is resized.


Relative
(CSS3 only)

(CSS3 only)
Relative
(CSS3 only)
(CSS3 only)


Absolute Units
Unit

Description

Type

in

Inches

Absolute

cm

Centimeters

Absolute

mm

Millimeters

Absolute

pt

Points (equal to 1/72 of an inch)
Points (equal to 1/72 of an inch)

Absolute

pc

Pica (equal to 1/6 of an inch)

Absolute



Comments in CSS
It is often helpful to add comments to your style
p
y
y
sheets. Comments take the form:
/* comment goes here */



Section 3 of 7

LOCATION OF STYLES


Actually there are three …
Different types of style sheet

Author‐created style sheets (what we are learning in
y
(
g
this presentation).
User style sheets allow the individual user to tell the
browser to display pages using that individual’s own
custom style sheet. This option is available in a
browser usually in its accessibility options area.
The browser style sheet defines the default styles the
browser uses for each HTML element.



Style Locations
Author Created CSS style rules can be located in three different locations

CSS style rules can be located in three different
y
locations.
•

Inline

•

Embedded

•

External
You can combine all 3!



Inline Styles
Style rules placed within an HTML element via the style attribute

An inline style only affects the element it is defined
An inline style only affects the element it is defined
within and will override any other style definitions for
the properties used in the inline style.
Using inline styles is generally discouraged since they
increase bandwidth and decrease maintainability.
Inline styles can however be handy for quickly testing
out a style change.



Embedded Style Sheet
Style rules placed within the <style> element inside the <head> element

While better than inline styles, using embedded styles
is also by and large discouraged.
Since each HTML document has its own <style>
element, it is more difficult to consistently style
multiple documents when using embedded styles.
p
g
y



External Style Sheet
Style rules placed within a external text file with the .css extension
css

This is by far the most common place to locate style
rules because it provides the best maintainability.
• Wh
When you make a change to an external style
k
h
l l
sheet, all HTML documents that reference that style
sheet will automatically use the updated version.
• The browser is able to cache the external style
sheet which can improve the performance of the site



Section 4 of 7

SELECTORS


Selectors
Things that make your life easier

When defining CSS rules, you will need to first need to
g
,y
use a selector to tell the browser which elements will
be affected.
CSS selectors allow you to select
CSS selectors allow you to select
•

individual elemenets

•

multiple HTML elements,
l i l HTML l

•

elements that belong together in some way, or

• elements that are positioned in specific ways in
the document hierarchy.
There are a number of different selector types.
There are a number of different selector types


Element Selectors
Selects all instances of a given HTML element

Uses the HTML element name.
You can select all elements by using the universal
element selector, which is the * (asterisk) character.



Grouped Selectors
Selecting multiple things

You can select a group of elements by separating the different
g p
y p
g
element names with commas.
This is a sensible way to reduce the size and complexity of your
CSS files, by combining multiple identical rules into a single
rule.
l


Reset

Grouped selectors are often used as a way to quickly reset
or remove browser defaults.
The goal of doing so is to reduce browser inconsistencies
with things such as margins, line heights, and font sizes.
These reset styles can be placed in their own css file
(perhaps called reset.css) and linked to the page before any
other external styles sheets.



Class Selectors
Simultaneously target different HTML elements

A class selector allows you to simultaneously target
y
y g
different HTML elements regardless of their position in
the document tree.
If a series of HTML element have been labeled with
the same class attribute value, then you can target
them for styling by using a class selector, which takes
the form: period (.) followed by the class name.



Class Selectors
<head>
<title>Share Your Travels </title>
<style>
.first {
font‐style: italic;
color: brown;
color: brown;
}
</style>
</head>
<body>
<h1 class="first">Reviews</h1>
<div>
<p class="first">By Ricardo on <time>September 15, 2012</time></p>
<p>Easy on the HDR buddy.</p>
</div>
<hr/>
<div>
<p class="first">By Susan on <time>October 1, 2012</time></p>
<p>I love Central Park.</p>
</div>
<hr/>
</body>
/b d



Id Selectors
Target a specific element by its id attribute

An id selector allows you to target a specific element
y
g
p
by its id attribute regardless of its type or position.
If an HTML element has been labeled with an id
attribute, then you can target it for styling by using an
id selector, which takes the form: pound/hash (#)
followed by the id name.

Note: You should only be using an id once per page
Note: You should only be using an id once per page



Id Selectors
<head lang "en">
lang= en >
<meta charset="utf-8">
<title>Share Your Travels -- New York - Central Park</title>
<style>
#latestComment {
font‐style: italic;
color: brown;
}
</style>
</head>
<body>
<h1>Reviews</h1>
<div id="latestComment">
<p>By Ricardo on <time>September 15, 2012</time></p>
</div>
<hr/>
<div>
<p>By Susan on <time>October 1, 2012</time></p>
</div>
<hr/>
/
</body>



Id versus Class Selectors
How to decide

Id selectors should only be used when referencing a
y
g
single HTML element since an id attribute can only be
assigned to a single HTML element.
Class selectors should be used when (potentially)
referencing several related elements.



Attribute Selectors
Selecting via presence of element attribute or by the value of an attribute

An attribute selector provides a way to select HTML
p
y
elements by either the presence of an element
attribute or by the value of an attribute.
This can be a very powerful technique, but because of
uneven support by some of the browsers, not all web
authors have used them.
Attribute selectors can be a very helpful technique in
the styling of hyperlinks and images.



Attribute Selectors
<head lang="en">
<meta charset="utf-8">
<title>Share Your Travels</title>
<titl >Sh
Y
T
l </titl >
<style>
[title] {
cursor: help;
padding‐bottom: 3px;
border‐bottom: 2px dotted blue;
text‐decoration: none;
text‐decoration: none;
}
</style>
</head>
<body>
<div>
g
g /
g /
p g
g /
<img src="images/flags/CA.png" title="Canada Flag" />
<h2><a href="countries.php?id=CA" title="see posts from Canada">
Canada</a>
</h2>
<p>Canada is a North American country consisting of … </p>
<div>
<img src="images/square/6114907897.jpg" title="At top of Sulpher Mountain">
<img src="images/square/6592317633.jpg" title="Grace Presbyterian Church">
<img src="images/square/6592914823.jpg" title="Calgary Downtown">
</div>
</div>
</body>



Pseudo Selectors
Select something that does not exist explicitly as an element

A pseudo‐element selector is a way to select
p
y
something that does not exist explicitly as an element
in the HTML document tree but which is still a
recognizable selectable object.
recognizable selectable object.
A pseudo‐class selector does apply to an HTML
element, but targets either a particular state or, in
CSS3, a variety of family relationships.
The most common use of this type of selectors is for
targeting link states.
i li k



Pseudo Selectors



Contextual Selectors
Select elements based on their ancestors descendants or siblings
ancestors, descendants,

A contextual selector (in CSS3 also called
(
combinators) allows you to select elements based on
their ancestors, descendants, or siblings.
That is, it selects elements based on their context or
their relation to other elements in the document tree.



Contextual Selectors
Selector

Matches

Example

Descendant

A specified element that is
contained somewhere within
another specified element

div p

A specified element that is a
direct child of the specified
element

div>h2

A specified element that is the
next sibling (i.e., comes directly
after) of the specified element.
A specified element that shares
the same parent as the specified
element.

h3+p

Child

Adjacent
Sibling
General Sibling


Selects a <p> element that is contained somewhere
within a <div> element. That is, the <p> can be any
descendant, not just a child.
Selects an <h2> element that is a child of a <div>
element.
Selects the first <p> after any <h3>.
h3~p

Selects all the <p> elements that share the same parent
as the
as the <h3>.


Descendant Selector
Selects all elements that are contained within another element

While some of these contextual selectors are used
relatively infrequently, almost all web authors find
themselves using descendant selectors.
A descendant selector matches all elements that are
contained within another element. The character used
to indicate descendant selection is the space
character.



Contextual Selectors in Action
<body>
<nav>
<ul>
<li><a href="#">Canada</a></li>
<li><a href= # >Germany</a></li>
href="#">Germany</a></li>
ul a:link { color: blue; }

<li><a href="#">United States</a></li>
</ul>

#main time { color: red; }

</nav>
<div id="main">
Comments as of <time>November 15, 2012</time>
#main>time { color: purple; }

#main div p:first-child {
color: green;
}

<div>
</div>
<hr/>
<div>
</div>
<hr/>
</div>
/di
<footer>
<ul>
<li><a href="#">Home</a> | </li>
<li><a href="#">Browse</a> | </li>
</ul>
</footer>
</body>



Section 5 of 7

THE CASCADE: HOW STYLES
INTERACT


Why Conflict Happens
In CSS that is

Because
• there are three different types of style sheets
(author‐created, user‐defined, and the default
browser style sheet),
• author‐created stylesheets can define multiple rules
for the same HTML element,
f th
HTML l
t
CSS has a system to help the browser determine how
to display elements when different style rules conflict.
to display elements when different style rules conflict



Cascade
How conflicting rules are handled in CSS

The “Cascade” in CSS refers to how conflicting rules
g
are handled.
The visual metaphor behind the term cascade is that
of a mountain stream progressing downstream over
rocks.
The downward movement of water down a cascade is
Th d
d
t f t d
d i
meant to be analogous to how a given style rule will
continue to take precedence with child elements.



Cascade Principles
CSS uses the following cascade principles to help it
g
p
p
p
deal with conflicts:
• inheritance,
• specificity,
• location



Inheritance
Cascade Principle #1

Many (but not all) CSS properties affect not only
y(
)
p p
y
themselves but their descendants as well.
Font, color, list, and text properties are inheritable.
Layout, sizing, border, background and spacing
properties are not.



Inheritance



Inheritance
How to force inheritance

It is possible to tell elements to inherit properties that
p
p p
are normally not inheritable.
div {
font-weight: bold;
margin: 50
i
50px;
border: 1pt solid green;
}
p {
border: inherit;
margin: inherit;
}
<h3>Reviews</h3>
<div>
</div>
<hr/>
<div>
</div>
<hr/>



Inheritance
div {
font-weight: bold;
margin: 50px;
border: 1pt solid green;
}

<html>

<head>

<meta> <title>

<body>

<h1>

<h2>

<p>

<a> <strong>

<img>

<h3>

<div>

<p>

<time>


<div>

<p> <p>

inherited
not inherited
not inherited

<p>

<p> <small>

<time>


Specificity

Specificity is how the browser determines which style
p
y
y
rule takes precedence when more than one style rule
could be applied to the same element.
The more specific the selector, the more it takes
precedence (i.e., overrides the previous definition).



Specificity
How it works

The way that specificity works in the browser is that
y
p
y
the browser assigns a weight to each style rule.
When several rules apply, the one with the greatest
weight takes precedence.



Specificity
These color and font‐weight
properties are inheritable and thus
potentially applicable to all the child
elements contained within the body.
elements contained within the body
However, because the <div> and <p>
elements also have the same
properties set, they override the value
defined for the <body> element
because their selectors (div and p) are
because their selectors (div and p) are
more specific.
Class selectors are more specific
than element selectors, and thus
take precedence and override
element selectors.

Id selectors are more specific than
class selectors, and thus take
class selectors and thus take
precedence and override class
selectors.


body {
font-weight: bold;
color: red;
}
div {
font-weight: normal;
color: magenta;
}
p {
color: green;
}
.last {
color: blue;
}
#verylast {
color: orange;
font-size: 16pt;
}

This text is not within a p element.
<p>Reviews</p>
<div>
<p>By Ricardo on <time>September 15 2012 /ti
B Ri
d
ti
S t b
15, 2012</time
This text is not within a p element.
</div>
<hr/>
<div>
</div>
<hr/>
<div>
<p class="last">By Dave on <time>October 15, 20
class last >By
<p class="last" id="verylast">Thanks for postin
</div>
<hr/>


Specificity Algorithm
The algorithm that is used to determine specificity is :

First count 1 if the declaration is from a 'style' attribute
y
in the HTML, 0 otherwise (let that value = a).
Count the number of ID attributes in the selector (let
that value = b).
Count the number of other attributes and pseudo‐
classes in the selector (let that value = c).
l
i th
l t (l t th t l
)
Count the number of element names and pseudo‐
elements in the selector (let that value = d).
elements in the selector (let that value = d)
Finally, concatenate the four numbers a+b+c+d
g
p
y
together to calculate the selector’s specificity.



Specificity Algorithm



Location

When inheritance and specificity cannot determine
p
y
style precedence, the principle of location will be
used.
The principle of location is that when rules have the
same specificity, then the latest are given more
weight.



Location

Can you guess what will be the color of the sample text ?


Location
What color would the sample text be if there wasn t an inline style definition?
What color would the sample text be if there wasn’t an inline style definition?



Location
There s
There’s always an exception

There is one exception to the principle of location.
p
p
p
If a property is marked with !important in an author‐
created style rule, then it will override any other
author‐created style regardless of its location.
The only exception is a style marked with !important
in an user style sheet; such a rule will override all
i
t l h t
h
l ill
id ll
others.



Section 6 of 7

THE BOX MODEL


The Box Model
Time to think inside the box

In CSS, all HTML elements exist within an element box.
,
It is absolutely essential that you familiarize yourself
with the terminology and relationship of the CSS
properties within the element box.



The Box Model



Background
Box Model Property #1

The background color or image of an element fills an
g
g
element out to its border (if it has one that is).
In contemporary web design, it has become extremely
common too use CSS to display purely presentational
images (such as background gradients and patterns,
decorative images, etc) rather than using the <img>
element.



Background Properties
Property

Description

background

A combined short‐hand property that allows you to set the background values
in one property. While you can omit properties with the short‐hand, do
remember that any omitted properties will be set to their default value.

background‐attachment

Specifies whether the background image scrolls with the document (default) or
remains fixed. Possible values are: fixed, scroll.

background‐color

Sets the background color of the element.

background‐image

Specifies the background image (which is generally a jpeg, gif, or png file) for
the element. Note that the URL is relative to the CSS file and not the HTML.
CSS3 introduced the ability to specify multiple background images.

background‐position
background position

Specifies where on the element the background image will be placed. Some
Specifies where on the element the background image will be placed Some
possible values include: bottom, center, left, and right. You can also supply a
pixel or percentage numeric position value as well. When supplying a numeric
value, you must supply a horizontal/vertical pair; this value indicates its
distance from the top left corner of the element.

background‐repeat

Determines whether the background image will be repeated. This is a common
technique for creating a tiled background (it is in fact the default behavior).
Possible values are: repeat, repeat‐x, repeat‐y, and no‐repeat.

background‐size

New to CSS3, this property lets you modify the size of the background image.



Background Repeat



Background Position



Borders
Box Model Property #2

Borders provide a way to visually separate elements.
p
y
y p
You can put borders around all four sides of an
element, or just one, two, or three of the sides.



Borders
Property

Description

border

A combined short‐hand property that allows you to set the style,
width, and color of a border in one property. The order is important
and must be:
and must be:
border‐style border‐width border‐color

border style
border‐style

Specifies the line type of the border. Possible values are:
Specifies the line type of the border. Possible values are: solid,
,
dotted, dashed, double, groove, ridge, inset, and outset.

border‐width

The width of the border in a unit (but not percents). A variety of
keywords (
keywords (thin, medium, etc) are also supported.
etc) are also supported

border‐color

The color of the border in a color unit.
The radius of a rounded corner.
The radius of a rounded corner.
The URL of an image to use as a border.

border radius
border‐radius
border‐image



Shortcut notation
TRBL

With border, margin, and padding properties, there
,
g ,
p
gp p
,
are long‐form and shortcut methods to set the 4 sides
border-top-color: red;
border-right-color:
border right color: green;
border-bottom-color: yellow;
border-left-color: blue;

/* sets just the top side */
/* sets just the right side */
/* sets just the right side */
/* sets just the bottom side */
/* sets just the left side */

border-color: red;

/* sets all four sides to red */

border-color: red green orange blue;
g
g
;

/
/* sets all four sides differently */
f
ff
y /

When using this multiple values shortcut, they are applied in clockwise order starting at the top.
Thus the order is: top right bottom left.



Margins and Padding
Box Model Properties #3 and #4



Margins
Why they will cause you trouble
trouble.
p {
border: solid 1pt red;
margin: 0;
padding: 0;
}

Did you notice that the space
between paragraphs one and two and
between two and three is the same
between two and three is the same
as the space before paragraph one
and after paragraph three?
This is due to the fact that adjoining
vertical margins collapse.


p {
margin: 30px;
padding: 0;
}

p {
margin: 30px;
padding: 30px;
}


Collapsing Margins
1

90px
50px
p
50px

4

50px

2

90px
50px
50px

5

50px

3

90px

<div>
<p>Every CSS rule ...</p>
<p>Every CSS rule ...</p>
</div>
<div>
<p>In CSS, the adjoining ... </p>
<p>In CSS, the adjoining ... </p>
</div>
div {
border: dotted 1pt green;
padding: 0;
margin: 90px 20px;
}
p {
padding: 0;
margin: 50px 20px;
}

If overlapping margins did not collapse, then margin space for
would be 180p (90pixels for the bottom margin of the first <div> +
90 pixels for the top margin of the second <div>), while the
margins and for would be 100px.
However, as you can see this is not the case.


Collapsing Margins
How it works

When the vertical margins of two elements touch,
g
,
• the largest margin value of the elements will be
displayed
• the smaller margin value will be collapsed to zero.
Horizontal margins, on the other hand, never collapse.
Horizontal margins on the other hand never collapse
To complicate matters even further, there are a large
number of special cases in which adjoining vertical
margins do not collapse.



Width and Height

The width and height properties specify the size of the
g p p
p y
element’s content area.
Perhaps the only rival for collapsing margins in
troubling our students, box dimensions have a number
of potential issues.



Width and Height
Potential Problem #1

Only block‐level elements and non‐text inline
y
elements such as images have a width and height that
you can specify.
By default the width of and height of elements is the
By default the width of and height of elements is the
actual size of the content.
For text,
• this is determined by the font size and font face;
For images,
For images,
• the width and height of the actual image in pixels
determines the element box’s dimensions.



Width and Height
Potential Problem #2

Since the width and the height refer to the size of the
g
content area, by default, the total size of an element is
equal to not only its content area, but also to the sum
of its padding, borders, and margins.
of its padding, borders, and margins.



Default



Width and Height
p {
background-color: silver;
}

100px
p {
background-color: silver;
width: 200px;
height: 100px;
}



Overflow Property
overflow: visible;

overflow: hidden;

overflow: scroll;
fl
ll

overflow: auto;



Sizing Elements
Time to embrace ems and percentages

While the previous examples used pixels for its
p
p
p
measurement, many contemporary designers prefer to
use percentages or em units for widths and heights.
• When you use percentages, the size is relative to
the size of the parent element.
• Wh
When you use ems, the size of the box is relative to
th i
f th b i l ti t
the size of the text within it.
The rationale behind using these relative measures is
The rationale behind using these relative measures is
to make one’s design scalable to the size of the
browser or device that is viewing it.



Developer Tools
Help is on the way

Developer tools in current browsers make it
p
significantly easier to examine and troubleshot CSS
than was the case a decade ago.
You can use the various browsers’ CSS inspection tools
to examine, for instance, the box values for a selected
element.



Developer Tools



Section 7 of 7

TEXT STYLING


Text Properties
Two basic types

CSS provides two types of properties that affect text.
p
yp
p p
• font properties that affect the font and its
appearance.
• paragraph properties that affect the text in a
similar way no matter which font is being used.



Font-Family
A few issues here

A word processor on a desktop machine can make use
p
p
of any font that is installed on the computer; browsers
are no different.
However, just because a given font is available on the
web developer’s computer, it does not mean that that
same font will be available for all users who view the
site.
For this reason, it is conventional to supply a so‐called
web font stack, that is, a series of alternate fonts to
bf
k h i
i
f l
f
use in case the original font choice in not on the user’s
computer.



Specifying the Font-Family



Generic Font-Family
The font‐family property supports five different
generic families.
The browser supports a typeface from each family.
Generic
Font‐Family
Name

serif

serif
if

Without
("sans") serif

sans-serif

This
This
This

monospace

This
hi

In a monospace font,
I
f t
each letter has the
same width

In a regular,
proportionally‐spaced
font, each letter has a
variable width

cursive

fantasy


Decorative and cursive fonts
vary from system to system;
rarely used as a result.


@font-face
The future is now

Over the past few years, the most recent browser
p
y
,
versions have begun to support the @font‐face
selector in CSS.
This selector allows you to use a font on your site even
if it is not installed on the end user’s computer.
Due to the on‐going popularity of open source font
D t th
i
l it f
f t
sites such as Google Web Fonts
(http://www.google.com/webfonts) and Font Squirrel
(http://www.fontsquirrel.com/), @font‐face seems to
(h //
f
i l
/) @f
f
have gained a critical mass of widespread usage.



Font Sizes
Mo control mo problems
control,

The issue of font sizes is unfortunately somewhat
y
tricky.
In a print‐based program such as a word processor,
specifying a font size in points is unproblematic.
specifying a font size in points is unproblematic
However, absolute units such as points and inches do
y
p
not translate very well to pixel‐based devices.
Somewhat surprisingly, pixels are also a problematic
unit.
Newer mobile devices in recent years have been
increasing pixel densities so that a given CSS pixel
does not correlate to a single device pixel.



Font Sizes
Welcome ems and percents again

If we wish to create web layouts that work well on
y
different devices, we should learn to use relative units
such as em units or percentages for our font sizes (and
indeed for other sizes in CSS as well).
indeed for other sizes in CSS as well).
One of the principles of the web is that the user
should be able to change the size of the text if he or
she so wishes to do so.
Using percentages or em units ensures that this user
action will work.
i
ill
k



How to use ems and percents
When used to specify a font size, both em units and
p y
,
percentages are relative to the parent’s font size.



It might seem easy … but it’s not …
it s

While this looks pretty easy to master, things
p y
y
,
g
unfortunately can quickly become quite complicated.
Remember that percents and em units are relative to
their parents, so if the parent font size changes, this
affects all of its contents.



ems and percents



The rem unit
Solution to font sizing hassles?

CSS3 now supports a new relative measure, the rem
pp
,
(for root em unit).
This unit is always relative to the size of the root
element (i.e., the <html> element).
However, since Internet Explorer prior to version 9 do
not support the rem units, you need to provide some
t
t th
it
dt
id
type of fallback for those browsers.



The rem unit
/* using 16px scale */
body { font-size:
p {
font-size:
font-size:
}
h1
{ font-size:

100%; }
16px;
1rem;

/* for older browsers: won’t scale properly though */
/* for new browsers: scales and simple too */

2em; }

article { font-size: 75% }

div


{ font size: 75% }
font-size:

/* h1 = 2 * 16 * 0.75 = 24px
p = 1 * 16 = 16px */
/* h1 = 2 * 16 * 0.75 * 0.75 = 18px
/* h1
2 * 16 * 0 75 * 0 75
18px
p = 1 * 16 = 16px
*/


What you’ve learned

1

What is CSS?

2

CSS Syntax

3

Location of Styles
y

4

Selectors

5

The Cascade: How
Styles Interact

6

The Box Model

7

CSS Text Styling



Buy the book, or
y
Find out more at

www.funwebdev.com


Textbook by Prentice Hall
Textbook to be published by Pearson Ed in early 2014
Fundamentals of http://www.funwebdev.com
Web Development
http://www.funwebdev.com

CSS: Introduction

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