CSS How To...

When a browser reads a style sheet, it will format the HTML document according to the information in the style sheet.

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

With an external style sheet, you can change the look of an entire website by changing just one file!

Each page must include a reference to the external style sheet file inside the <link> element. The <link> element goes inside the <head> section:

Example

An external style sheet can be written in any text editor. The file should not contain any html tags. The style sheet file must be saved with a .css extension.

Here is how the "mystyle.css" looks:

body {
    background-color: lightblue;
}

h1 {
    color: navy;
    margin-left: 20px;
}

Note: Do not add a space between the property value and the unit (such as margin-left: 20 px;). The correct way is: margin-left: 20px;

Internal Style Sheet

An internal style sheet may be used if one single page has a unique style.

Internal styles are defined within the <style> element, inside the <head> section of an HTML page:

Example

<head>
<style>
body {
    background-color: linen;
}

h1 {
    color: maroon;
    margin-left: 40px;
}
</style>
</head>

Inline Styles

An inline style may be used to apply a unique style for a single element.

To use inline styles, add the style attribute to the relevant element. The style attribute can contain any CSS property.

The example below shows how to change the color and the left margin of a <h1> element:

Example

<h1 style="color:blue;margin-left:30px;">This is a heading</h1>

Tip: An inline style loses many of the advantages of a style sheet (by mixing content with presentation). Use this method sparingly.

Multiple Style Sheets

If some properties have been defined for the same selector (element) in different style sheets, the value from the last read style sheet will be used.

Example

Assume that an external style sheet has the following style for the <h1> element:

h1 {
color: navy;
}

then, assume that an internal style sheet also has the following style for the <h1> element:

h1 {
color: orange;
}

If the internal style is defined after the link to the external style sheet, the <h1> elements will be "orange":

Example

<head>
<link rel="stylesheet" type="text/css" href="mystyle.css">
<style>
h1 {
color: orange;
}
</style>
</head>

However, if the internal style is defined before the link to the external style sheet, the <h1> elements will be "navy":

Example

<head>
<style>
h1 {
color: orange;
}
</style>
<link rel="stylesheet" type="text/css" href="mystyle.css">
</head>

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 one has the highest priority:

Inline style (inside an HTML element)
External and internal style sheets (in the head section)
Browser default

So, an inline style (inside a specific 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 a browser default value.

CSS Backgrounds

The CSS background properties are used to define the background effects for elements.

CSS background properties:

background-color
background-image
background-repeat
background-attachment
background-positio

Background Color

The background-color property specifies the background color of an element.

The background color of a page is set like this:

Example

body {
background-color: lightblue;
}

With CSS, a color is most often specified by:

a valid color name - like "red"
a HEX value - like "#ff0000"
an RGB value - like "rgb(255,0,0)"

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: green;
}

div {
    background-color: lightblue;
}

p {
    background-color: yellow;
}

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 hardly readable:

Example

body {
background-image: url("bgdesert.jpg");
}

Note: When using a background image, use an image that does not disturb the text.

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("gradient_bg.png");
}

If the image above is repeated only horizontally (background-repeat: repeat-x;), the background will look better:

Example

body {
background-image: url("gradient_bg.png");
background-repeat: repeat-x;
}

Tip: To repeat an image vertically, set background-repeat: repeat-y;

Background Image - Set position and no-repeat

Showing the background image only once is also 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 Image - Fixed position

To specify that the background image should be fixed (will not scroll with the rest of the page), use the background-attachment property:

Example

body {
    background-image: url("img_tree.png");
    background-repeat: no-repeat;
    background-position: right top;
    background-attachment: fixed;
}

Background - Shorthand property

To shorten the code, it is also possible to specify all the background properties in one single property. This is called a shorthand property.

The shorthand property for background is 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 other ones are in this order.

All CSS Background Properties

Property	Description
background	Sets all the background properties in one declaration
background-attachment	Sets whether a background image is fixed or scrolls with the rest of the page
background-color	Sets the background color of an element
background-image	Sets the background image for an element
background-position	Sets the starting position of a background image
background-repeat	Sets how a background image will be repeated