What
You Should Already Know
Before you continue you should have
a basic understanding of the following:
If you want to study these subjects
first, find the tutorials on our Home page.
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
CSS
Demo
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 (W3C) 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
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;
}
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;
}
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:
hr {color:sienna;}
p {margin-left:20px;}
body {background-image:url("images/back40.gif");}
Do not leave spaces
between the property value and the units! "margin-left:20 px"
(instead of "margin-left:20px") will work in IE, but not in Firefox
or Opera.
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>
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:
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:
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.
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
Tip: Even multiple external style sheets can be referenced inside a
single HTML document.
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)
So, an inline style (inside an HTML element) has the highest priority, which
means that it will override a style defined inside the <head> tag, or in
an external style sheet, or in a browser (a default value).
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 Id and Class
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;
}
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 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"
Look at
CSS
Color Values for a complete list of possible color values.
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;}
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');
}
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 - 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;
}
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 - 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 are:
- 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
More Examples
How to set a fixed background image
This example demonstrates how to set a fixed background image. The image will
not scroll with the rest of the page.
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
|
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);}
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;}
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;}
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;}
Text
Indentation
The text-indentation property is
used to specify the indentation of the first line of a text.
Example
p {text-indent:50px;}
More
Examples
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;}
For more commonly used font combinations, look at our
Web Safe Font
Combinations.
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;}
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;}
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 */
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;}
Our code now works great! It shows the same text size in all browsers, and
allows all browsers to zoom or resize the text!
More Examples
Set the boldness of the font
This example demonstrates how to set the boldness of a font.
Set the variant of the font
This example demonstrates how to set the variant of a font.
All the font properties in one declaration
This example demonstrates how to use the shorthand property for setting all of
the font properties in one declaration.
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
|
