CSS Introduction
What
You Should Already Know
Before you continue you should have
a basic understanding of the following:
- HTML / XHTML
What
is CSS?
- CSS stands for Cascading Style Sheets
- Styles define how to display HTML elements
- Styles were added to HTML 4.0 to solve a problem
- External Style Sheets can save a lot of work
- External Style Sheets are stored in CSS files
Styles
Solved a Big Problem
HTML was never intended to contain
tags for formatting a document.
HTML was intended to define the
content of a document, like:
<h1>This is a
heading</h1>
<p>This is a
paragraph.</p>
When tags like <font>, and
color attributes were added to the HTML 3.2 specification, it started a
nightmare for web developers. Development of large web sites, where fonts and
color information were added to every single page, became a long and expensive
process.
To solve this problem, the World
Wide Web Consortium created CSS.
In HTML 4.0, all formatting could be
removed from the HTML document, and stored in a separate CSS file.
All browsers support CSS today.
CSS
Saves a Lot of Work!
CSS defines HOW HTML elements are to
be displayed.
Styles are normally saved in
external .css files. External style sheets enable you to change the appearance
and layout of all the pages in a Web site, just by editing one single file!
CSS Syntax
Examples
CSS
Syntax
A CSS rule has two main parts: a
selector, and one or more declarations:
The selector is normally the HTML
element you want to style.
Each declaration consists of a
property and a value.
The property is the style attribute
you want to change. Each property has a value.
CSS
Example
A CSS declaration always ends with a
semicolon, and declaration groups are surrounded by curly brackets:
p {color:red;text-align:center;}
To make the CSS more readable, you
can put one declaration on each line, like this:
Example
p
{
color:red;
text-align:center;
}
{
color:red;
text-align:center;
}
CSS
Comments
Comments are used to explain your
code, and may help you when you edit the source code at a later date. Comments
are ignored by browsers.
A CSS comment begins with
"/*", and ends with "*/", like this:
/*This is a comment*/
p
{
text-align:center;
/*This is another comment*/
color:black;
font-family:arial;
}
p
{
text-align:center;
/*This is another comment*/
color:black;
font-family:arial;
}
The
id and class Selectors
In addition to setting a style for a
HTML element, CSS allows you to specify your own selectors called
"id" and "class".
The
id Selector
The id selector is used to specify a
style for a single, unique element.
The id selector uses the id
attribute of the HTML element, and is defined with a "#".
The style rule below will be applied
to the element with id="para1":
Example
#para1
{
text-align:center;
color:red;
}
{
text-align:center;
color:red;
}
Do NOT start an ID name with
a number! It will not work in Mozilla/Firefox.
The
class Selector
The class selector is used to
specify a style for a group of elements. Unlike the id selector, the class
selector is most often used on several elements.
This allows you to set a particular
style for many HTML elements with the same class.
The class selector uses the HTML
class attribute, and is defined with a "."
In the example below, all HTML
elements with class="center" will be center-aligned:
Example
.center
{text-align:center;}
You can also specify that only
specific HTML elements should be affected by a class.
In the example below, all p elements
with class="center" will be center-aligned:
Example
p.center
{text-align:center;}
Do NOT start a class name
with a number! This is only supported in Internet Explorer.
CSS How To...
When a browser reads a style sheet, it will format the document
according to it.
Three Ways to Insert CSS
There are three ways of inserting a style sheet:- External style sheet
- Internal style sheet
- Inline style
External Style Sheet
An external style sheet is ideal when the style is applied to many pages. With an external style sheet, you can change the look of an entire Web site by changing one file. Each page must link to the style sheet using the <link> tag. The <link> tag goes inside the head section:
<head>
<link rel="stylesheet" type="text/css" href="mystyle.css" />
</head>
An external style sheet can be written in any text editor. The file should
not contain any html tags. Your style sheet should be saved with a .css
extension. An example of a style sheet file is shown below:<link rel="stylesheet" type="text/css" href="mystyle.css" />
</head>
hr
{color:sienna;}
p {margin-left:20px;}
body {background-image:url("images/back40.gif");}
Do not add a space between the property value and the unit (such as
margin-left:20 px). The correct way is: margin-left:20pxp {margin-left:20px;}
body {background-image:url("images/back40.gif");}
Internal Style Sheet
An internal style sheet should be used when a single document has a unique style. You define internal styles in the head section of an HTML page, by using the <style> tag, like this:
<head>
<style type="text/css">
hr {color:sienna;}
p {margin-left:20px;}
body {background-image:url("images/back40.gif");}
</style>
</head>
<style type="text/css">
hr {color:sienna;}
p {margin-left:20px;}
body {background-image:url("images/back40.gif");}
</style>
</head>
Inline Styles
An inline style loses many of the advantages of style sheets by mixing content with presentation. Use this method sparingly!To use inline styles you use the style attribute in the relevant tag. The style attribute can contain any CSS property. The example shows how to change the color and the left margin of a paragraph:
<p
style="color:sienna;margin-left:20px">This is a
paragraph.</p>
Multiple Style Sheets
If some properties have been set for the same selector in different style sheets, the values will be inherited from the more specific style sheet.For example, an external style sheet has these properties for the h3 selector:
h3
{
color:red;
text-align:left;
font-size:8pt;
}
And an internal style sheet has these properties for the h3 selector:{
color:red;
text-align:left;
font-size:8pt;
}
h3
{
text-align:right;
font-size:20pt;
}
If the page with the internal style sheet also links to the external style
sheet the properties for h3 will be:{
text-align:right;
font-size:20pt;
}
color:red;
text-align:right;
font-size:20pt;
The color is inherited from the external style sheet and the text-alignment
and the font-size is replaced by the internal style sheet.text-align:right;
font-size:20pt;
Multiple Styles Will Cascade into One
Styles can be specified:- inside an HTML element
- inside the head section of an HTML page
- in an external CSS file
Cascading order
What style will be used when there is more than one style specified for an HTML element?Generally speaking we can say that all the styles will "cascade" into a new "virtual" style sheet by the following rules, where number four has the highest priority:
- Browser default
- External style sheet
- Internal style sheet (in the head section)
- Inline style (inside an HTML element)
Note: If the link to the external style sheet is placed after the internal style sheet in HTML <head>, the external style sheet will override the internal style sheet!
CSS Background
CSS background properties are used to define the background
effects of an element.
CSS
properties used for background effects:
- background-color
- background-image
- background-repeat
- background-attachment
- background-position
Background
Color
The background-color property
specifies the background color of an element.
The background color of a page is
defined in the body selector:
Example
body
{background-color:#b0c4de;}
With CSS, a color is most often
specified by:
- a HEX value - like "#ff0000"
- an RGB value - like "rgb(255,0,0)"
- a color name - like "red"
In the example below, the h1, p, and
div elements have different background colors:
Example
h1
{background-color:#6495ed;}
p {background-color:#e0ffff;}
div {background-color:#b0c4de;}
p {background-color:#e0ffff;}
div {background-color:#b0c4de;}
Background
Image
The background-image property
specifies an image to use as the background of an element.
By default, the image is repeated so
it covers the entire element.
The background image for a page can
be set like this:
Example
body
{background-image:url('paper.gif');}
Below is an example of a bad
combination of text and background image. The text is almost not readable:
Example
body
{background-image:url('bgdesert.jpg');}
Background
Image - Repeat Horizontally or Vertically
By default, the background-image
property repeats an image both horizontally and vertically.
Some images should be repeated only
horizontally or vertically, or they will look strange, like this:
Example
body
{
background-image:url('gradient2.png');
}
{
background-image:url('gradient2.png');
}
If the image is repeated only
horizontally (repeat-x), the background will look better:
Example
body
{
background-image:url('gradient2.png');
background-repeat:repeat-x;
}
{
background-image:url('gradient2.png');
background-repeat:repeat-x;
}
Background
Image - Set position and no-repeat
When using a background image, use
an image that does not disturb the text.
Showing the image only once is
specified by the background-repeat property:
Example
body
{
background-image:url('img_tree.png');
background-repeat:no-repeat;
}
{
background-image:url('img_tree.png');
background-repeat:no-repeat;
}
In the example above, the background
image is shown in the same place as the text. We want to change the position of
the image, so that it does not disturb the text too much.
The position of the image is
specified by the background-position property:
Example
body
{
background-image:url('img_tree.png');
background-repeat:no-repeat;
background-position:right top;
}
{
background-image:url('img_tree.png');
background-repeat:no-repeat;
background-position:right top;
}
Background
- Shorthand property
As you can see from the examples
above, there are many properties to consider when dealing with backgrounds.
To shorten the code, it is also
possible to specify all the properties in one single property. This is called a
shorthand property.
The shorthand property for
background is simply "background":
Example
body {background:#ffffff
url('img_tree.png') no-repeat right top;}
When using the shorthand property
the order of the property values is:
- background-color
- background-image
- background-repeat
- background-attachment
- background-position
It does not matter if one of the
property values is missing, as long as the ones that are present are in this
order.
This example uses more advanced CSS.
Take a look: Advanced example
All
CSS Background Properties
|
Property
|
Description
|
|
Sets all the background properties
in one declaration
|
|
|
Sets whether a background image is
fixed or scrolls with the rest of the page
|
|
|
Sets the background color of an
element
|
|
|
Sets the background image for an
element
|
|
|
Sets the starting position of a
background image
|
|
|
Sets how a background image will
be repeated
|
CSS Text
text
formatting
This text is styled with some of the
text formatting properties. The heading uses the text-align, text-transform,
and color properties. The paragraph is indented, aligned, and the space between
characters is specified. The underline is removed from the link.
Text
Color
The color property is used to set
the color of the text.
With CSS, a color is most often
specified by:
- a HEX value - like "#ff0000"
- an RGB value - like "rgb(255,0,0)"
- a color name - like "red"
The default color for a page is
defined in the body selector.
Example
body {color:blue;}
h1 {color:#00ff00;}
h2 {color:rgb(255,0,0);}
h1 {color:#00ff00;}
h2 {color:rgb(255,0,0);}
For W3C compliant CSS: If you define
the color property, you must also define the background-color property.
Text
Alignment
The text-align property is used to
set the horizontal alignment of a text.
Text can be centered, or aligned to
the left or right, or justified.
When text-align is set to
"justify", each line is stretched so that every line has equal width,
and the left and right margins are straight (like in magazines and newspapers).
Example
h1 {text-align:center;}
p.date {text-align:right;}
p.main {text-align:justify;}
p.date {text-align:right;}
p.main {text-align:justify;}
Text
Decoration
The text-decoration property is used
to set or remove decorations from text.
The text-decoration property is
mostly used to remove underlines from links for design purposes:
Example
a {text-decoration:none;}
It can also be used to decorate
text:
Example
h1 {text-decoration:overline;}
h2 {text-decoration:line-through;}
h3 {text-decoration:underline;}
h4 {text-decoration:blink;}
h2 {text-decoration:line-through;}
h3 {text-decoration:underline;}
h4 {text-decoration:blink;}
It is not recommended to underline
text that is not a link, as this often confuses users.
Text
Transformation
The text-transform property is used
to specify uppercase and lowercase letters in a text.
It can be used to turn everything
into uppercase or lowercase letters, or capitalize the first letter of each
word.
Example
p.uppercase
{text-transform:uppercase;}
p.lowercase {text-transform:lowercase;}
p.capitalize {text-transform:capitalize;}
p.lowercase {text-transform:lowercase;}
p.capitalize {text-transform:capitalize;}
Text
Indentation
The text-indentation property is
used to specify the indentation of the first line of a text.
Example
p {text-indent:50px;}
All
CSS Text Properties
|
Property
|
Description
|
|
Sets the color of text
|
|
|
Specifies the text
direction/writing direction
|
|
|
Increases or decreases the space
between characters in a text
|
|
|
Sets the line height
|
|
|
Specifies the horizontal alignment
of text
|
|
|
Specifies the decoration added to
text
|
|
|
Specifies the indentation of the
first line in a text-block
|
|
|
text-shadow
|
Specifies the shadow effect added
to text
|
|
Controls the capitalization of
text unicode-bidi
|
|
|
Sets the vertical alignment of an
element
|
|
|
Specifies how white-space inside
an element is handled
|
|
|
Increases or decreases the space
between words in a text
|
CSS Font
CSS
font properties define the font family, boldness, size, and the style of a
text.
Difference
Between Serif and Sans-serif Fonts
On computer screens, sans-serif
fonts are considered easier to read than serif fonts.
CSS
Font Families
In CSS, there are two types of font
family names:
- generic family - a group of font families with a similar look (like "Serif" or "Monospace")
- font family - a specific font family (like "Times New Roman" or "Arial")
|
Generic family
|
Font family
|
Description
|
|
Serif
|
Times New Roman
Georgia |
Serif fonts have small
lines at the ends on some characters
|
|
Sans-serif
|
Arial
Verdana |
"Sans" means
without - these fonts do not have the lines at the ends of characters
|
|
Monospace
|
Courier New
Lucida Console |
All monospace characters
have the same width
|
Font
Family
The font family of a text is set
with the font-family property.
The font-family property should hold
several font names as a "fallback" system. If the browser does not
support the first font, it tries the next font.
Start with the font you want, and
end with a generic family, to let the browser pick a similar font in the
generic family, if no other fonts are available.
Note: If the name of a font family is more than one word, it
must be in quotation marks, like font-family: "Times New Roman".
More than one font family is
specified in a comma-separated list:
Example
p{font-family:"Times
New Roman", Times, serif;}
Font
Style
The font-style property is mostly
used to specify italic text.
This property has three values:
- normal - The text is shown normally
- italic - The text is shown in italics
- oblique - The text is "leaning" (oblique is very similar to italic, but less supported)
Example
p.normal {font-style:normal;}
p.italic {font-style:italic;}
p.oblique {font-style:oblique;}
p.italic {font-style:italic;}
p.oblique {font-style:oblique;}
Font
Size
The font-size property sets the size
of the text.
Being able to manage the text size
is important in web design. However, you should not use font size adjustments
to make paragraphs look like headings, or headings look like paragraphs.
Always use the proper HTML tags,
like <h1> - <h6> for headings and <p> for paragraphs.
The font-size value can be an
absolute, or relative size.
Absolute size:
- Sets the text to a specified size
- Does not allow a user to change the text size in all browsers (bad for accessibility reasons)
- Absolute size is useful when the physical size of the output is known
Relative size:
- Sets the size relative to surrounding elements
- Allows a user to change the text size in browsers
If you do not specify a font size,
the default size for normal text, like paragraphs, is 16px (16px=1em).
Set
Font Size With Pixels
Setting the text size with pixels
gives you full control over the text size:
Example
h1 {font-size:40px;}
h2 {font-size:30px;}
p {font-size:14px;}
h2 {font-size:30px;}
p {font-size:14px;}
The example above allows Internet
Explorer 9, Firefox, Chrome, Opera, and Safari to resize the text.
Note: The example above does not work in IE, prior version 9.
The text can be resized in all
browsers using the zoom tool (however, this resizes the entire page, not just
the text).
Set
Font Size With Em
To avoid the resizing problem with
older versions of Internet Explorer, many developers use em instead of pixels.
The em size unit is recommended by
the W3C.
1em is equal to the current font
size. The default text size in browsers is 16px. So, the default size of 1em is
16px.
The size can be calculated from
pixels to em using this formula: pixels/16=em
Example
h1 {font-size:2.5em;} /*
40px/16=2.5em */
h2 {font-size:1.875em;} /* 30px/16=1.875em */
p {font-size:0.875em;} /* 14px/16=0.875em */
h2 {font-size:1.875em;} /* 30px/16=1.875em */
p {font-size:0.875em;} /* 14px/16=0.875em */
In the example above, the text size
in em is the same as the previous example in pixels. However, with the em size,
it is possible to adjust the text size in all browsers.
Unfortunately, there is still a
problem with older versions of IE. The text becomes larger than it should when
made larger, and smaller than it should when made smaller.
Use
a Combination of Percent and Em
The solution that works in all
browsers, is to set a default font-size in percent for the <body>
element:
Example
body {font-size:100%;}
h1 {font-size:2.5em;}
h2 {font-size:1.875em;}
p {font-size:0.875em;}
h1 {font-size:2.5em;}
h2 {font-size:1.875em;}
p {font-size:0.875em;}
Our code now works great! It shows
the same text size in all browsers, and allows all browsers to zoom or resize
the text!
All CSS Font Properties
|
Property
|
Description
|
|
Sets all the font properties in
one declaration
|
|
|
Specifies the font family for text
|
|
|
Specifies the font size of text
|
|
|
Specifies the font style for text
|
|
|
Specifies whether or not a text
should be displayed in a small-caps font
|
|
|
Specifies the weight of a font
|
CSS Links
Links can be styled in different
ways.
Styling
Links
Links can be styled with any CSS
property (e.g. color, font-family, background, etc.).
Special for links are that they can
be styled differently depending on what state they are in.
The four links states are:
- a:link - a normal, unvisited link
- a:visited - a link the user has visited
- a:hover - a link when the user mouses over it
- a:active - a link the moment it is clicked
Example
a:link
{color:#FF0000;} /* unvisited link */
a:visited {color:#00FF00;} /* visited link */
a:hover {color:#FF00FF;} /* mouse over link */
a:active {color:#0000FF;} /* selected link */
a:visited {color:#00FF00;} /* visited link */
a:hover {color:#FF00FF;} /* mouse over link */
a:active {color:#0000FF;} /* selected link */
When setting the style for several
link states, there are some order rules:
- a:hover MUST come after a:link and a:visited
- a:active MUST come after a:hover
Common
Link Styles
In the example above the link
changes color depending on what state it is in.
Lets go through some of the other
common ways to style links:
Text
Decoration
The text-decoration property is
mostly used to remove underlines from links:
Example
a:link
{text-decoration:none;}
a:visited {text-decoration:none;}
a:hover {text-decoration:underline;}
a:active {text-decoration:underline;}
a:visited {text-decoration:none;}
a:hover {text-decoration:underline;}
a:active {text-decoration:underline;}
Background
Color
The background-color property
specifies the background color for links:
Example
a:link {background-color:#B2FF99;}
a:visited {background-color:#FFFF85;}
a:hover {background-color:#FF704D;}
a:active {background-color:#FF704D;}
a:visited {background-color:#FFFF85;}
a:hover {background-color:#FF704D;}
a:active {background-color:#FF704D;}
CSS Lists
The
CSS list properties allow you to:
·
Set different list item markers for
ordered lists
·
Set different list item markers for
unordered lists
·
Set an image as the list item marker
List
In HTML, there are two types of
lists:
- unordered lists - the list items are marked with bullets
- ordered lists - the list items are marked with numbers or letters
With CSS, lists can be styled
further, and images can be used as the list item marker.
Different
List Item Markers
The type of list item marker is
specified with the list-style-type property:
Example
ul.a {list-style-type:
circle;}
ul.b {list-style-type: square;}
ol.c {list-style-type: upper-roman;}
ol.d {list-style-type: lower-alpha;}
ul.b {list-style-type: square;}
ol.c {list-style-type: upper-roman;}
ol.d {list-style-type: lower-alpha;}
Some of the values are for unordered
lists, and some for ordered lists.
An
Image as The List Item Marker
To specify an image as the list item
marker, use the list-style-image property:
Example
ul
{
list-style-image: url('sqpurple.gif');
}
{
list-style-image: url('sqpurple.gif');
}
The example above does not display
equally in all browsers. IE and Opera will display the image-marker a little
bit higher than Firefox, Chrome, and Safari.
If you want the image-marker to be
placed equally in all browsers, a crossbrowser solution is explained below.
Crossbrowser
Solution
The following example displays the
image-marker equally in all browsers:
Example
ul
{
list-style-type: none;
padding: 0px;
margin: 0px;
}
ul li
{
background-image: url(sqpurple.gif);
background-repeat: no-repeat;
background-position: 0px 5px;
padding-left: 14px;
}
{
list-style-type: none;
padding: 0px;
margin: 0px;
}
ul li
{
background-image: url(sqpurple.gif);
background-repeat: no-repeat;
background-position: 0px 5px;
padding-left: 14px;
}
Example explained:
- For ul:
- Set the list-style-type to none to remove the list item marker
- Set both padding and margin to 0px (for cross-browser compatibility)
- For all li in ul:
- Set the URL of the image, and show it only once (no-repeat)
- Position the image where you want it (left 0px and down 5px)
- Position the text in the list with padding-left
List
- Shorthand property
It is also possible to specify all
the list properties in one, single property. This is called a shorthand
property.
The shorthand property used for
lists, is the list-style property:
Example
ul
{
list-style: square url("sqpurple.gif");
}
{
list-style: square url("sqpurple.gif");
}
When using the shorthand property,
the order of the values are:
- list-style-type
- list-style-position (for a description, see the CSS properties table below)
- list-style-image
It does not matter if one of the
values above are missing, as long as the rest are in the specified order.
All
CSS List Properties
|
Property
|
Description
|
|
Sets all the properties for a list
in one declaration
|
|
|
Specifies an image as the
list-item marker
|
|
|
Specifies if the list-item markers
should appear inside or outside the content flow
|
|
|
Specifies the type of list-item
marker
|
CSS Tables
The look of an HTML table can be
greatly improved with CSS:
|
Company
|
Contact
|
Country
|
|
Alfreds Futterkiste
|
Maria Anders
|
Germany
|
|
Berglunds snabbköp
|
Christina Berglund
|
Sweden
|
|
Centro comercial Moctezuma
|
Francisco Chang
|
Mexico
|
|
Ernst Handel
|
Roland Mendel
|
Austria
|
|
Island Trading
|
Helen Bennett
|
UK
|
|
Königlich Essen
|
Philip Cramer
|
Germany
|
|
Laughing Bacchus Winecellars
|
Yoshi Tannamuri
|
Canada
|
|
Magazzini Alimentari Riuniti
|
Giovanni Rovelli
|
Italy
|
|
North/South
|
Simon Crowther
|
UK
|
|
Paris spécialités
|
Marie Bertrand
|
France
|
|
The Big Cheese
|
Liz Nixon
|
USA
|
|
Vaffeljernet
|
Palle Ibsen
|
Denmark
|
Table
Borders
To specify table borders in CSS, use
the border property.
The example below specifies a black
border for table, th, and td elements:
Example
table, th, td
{
border: 1px solid black;
}
{
border: 1px solid black;
}
Notice that the table in the example
above has double borders. This is because both the table and the th/td elements
have separate borders.
To display a single border for the
table, use the border-collapse property.
Collapse
Borders
The border-collapse property sets
whether the table borders are collapsed into a single border or separated:
Example
table
{
border-collapse:collapse;
}
table,th, td
{
border: 1px solid black;
}
{
border-collapse:collapse;
}
table,th, td
{
border: 1px solid black;
}
Table
Width and Height
Width and height of a table is
defined by the width and height properties.
The example below sets the width of
the table to 100%, and the height of the th elements to 50px:
Example
table
{
width:100%;
}
th
{
height:50px;
}
{
width:100%;
}
th
{
height:50px;
}
Table
Text Alignment
The text in a table is aligned with
the text-align and vertical-align properties.
The text-align property sets the
horizontal alignment, like left, right, or center:
Example
td
{
text-align:right;
}
{
text-align:right;
}
The vertical-align property sets the
vertical alignment, like top, bottom, or middle:
Example
td
{
height:50px;
vertical-align:bottom;
}
{
height:50px;
vertical-align:bottom;
}
Table
Padding
To control the space between the
border and content in a table, use the padding property on td and th elements:
Example
td
{
padding:15px;
}
{
padding:15px;
}
Table
Color
The example below specifies the
color of the borders, and the text and background color of th elements:
Example
table, td, th
{
border:1px solid green;
}
th
{
background-color:green;
color:white;
}
{
border:1px solid green;
}
th
{
background-color:green;
color:white;
}
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