Applying CSS

When a browser reads a style sheet, it will format the 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:

<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. The style sheet file must be saved with a .css extension. An example of a style sheet file called “myStyle.css”, is shown below:

body {
    background-color: lightblue;
}

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

	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.

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

To use inline styles, add the style attribute to 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 <h1> element:

Example

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

Multiple Style Sheets

If some properties have been defined for the same selector in different style sheets, the value will be inherited from the more specific style sheet.

For example, assume that an external style sheet has the following properties for the <h1> element:

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

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

h1 {
    color: orange;   
}

If the page with the internal style sheet also links to the external style sheet the properties for the <h1> element will be:

color: orange;
margin-left: 20px;

The left margin is inherited from the external style sheet and the color is replaced by the internal style sheet.

Multiple Styles Will Cascade into One

Styles can be specified:

in an external CSS file
inside the <head> section of an HTML page
inside an HTML element

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 three has the highest priority:

Browser default
External and internal style sheets (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).

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