Three Ways to Insert CSS(浅析三种插入css的方法)
When a browser reads a style sheet, it will format the document according to it. There are three ways of inserting a style sheet:External style sheet, Internal style sheet and Inline style. Below are the details.
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:
<link rel="stylesheet" type="text/css" href="teststyle.css" />
</head>
p {margin-left:20px}
body {background-image:url("backimage.gif")}
Note: 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. Just define internal styles in the head section of an HTML page, by using the <style> tag, like this:
<style type="text/css">
hr {color:sienna}
p {margin-left:20px}
body {background-image:url("backimage.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:
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 h1 selector:
{
color:blue;
text-align:center;
font-size:8pt
}
And an internal style sheet has these properties for the h1 selector:
{
text-align:right;
font-size:20pt
}
text-align:right;
font-size:20pt
That is: The color is inherited from the external style sheet and the text-alignment and the font-size is replaced by the internal style sheet.
But note that: 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!
In addition:
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:
1. Browser default
2. External style sheet
3. Internal style sheet (in the head section)
4. 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).
