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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 CSS
- Internal CSS
- Inline CSS
External CSS
With an external style sheet, you can change the look of an entire website by changing just one file!
Each HTML page must include a reference to the external style sheet file inside the <link> element, inside the head section.
Example
External styles are defined within the <link> element, inside the <head> section of an HTML page:
<!DOCTYPE html> <html> <head> <link rel="stylesheet" href="mystyle.css"> </head> <body> <h1>This is a heading</h1> <p>This is a paragraph.</p> </body> </html>
An external style sheet can be written in any text editor, and must be saved with a .css extension.
The external .css file should not contain any HTML tags.
Here is how the "mystyle.css" file looks:
"mystyle.css"
body {
background-color: lightblue;
}
h1 {
color: navy;
margin-left: 20px;
}
Note: Do not add a space between the property value (20) and the unit
(px):
Incorrect (space): margin-left: 20 px;
Correct (no space): margin-left: 20px;
Internal CSS
An internal style sheet may be used if one single HTML page has a unique style.
The internal style is defined inside the <style> element, inside the head section.
Example
Internal styles are defined within the <style> element, inside the <head> section of an HTML page:
<!DOCTYPE html>
<html>
<head>
<style>
body {
background-color: linen;
}
h1 {
color: maroon;
margin-left: 40px;
}
</style>
</head>
<body>
<h1>This is a heading</h1>
<p>This is a paragraph.</p>
</body>
</html>
Inline CSS
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.
Example
Inline styles are defined within the "style" attribute of the relevant element:
<!DOCTYPE html> <html> <body> <h1 style="color:blue;text-align:center;">This is a heading</h1> <p style="color:red;">This is a paragraph.</p> </body> </html>
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.
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;
}
Example
If the internal style is defined after the link to the external style sheet, the <h1> elements will be "orange":
<head>
<link rel="stylesheet" type="text/css" href="mystyle.css">
<style>
h1 {
color: orange;
}
</style>
</head>
Example
However, if the internal style is defined before the link to the external style sheet, the <h1> elements will be "navy":
<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?
All the styles in a page 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 has the highest priority, and will override external and internal styles and browser defaults.
<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" type="text/css" href="mystyle.css">
<style>
body {background-color: linen;}
</style>
</head>
<body style="background-color: lavender">
<h1>Multiple Styles Will Cascade into One</h1>
<p>Here, the background color of the page is set with inline CSS, and also with an internal CSS, and also with an external CSS.</p>
<p>Try experimenting by removing styles to see how the cascading stylesheets work (try removing the inline CSS first, then the internal, then the external).</p>
</body>
</html>
标签：style,sheet,color,css08,element,How,Add,external,CSS From： https://www.cnblogs.com/emanlee/p/18221141