There are three ways of inserting a style sheet:
1. External style sheet
2. Internal style sheet
3. 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:
<link rel="stylesheet" type="text/css" href="mystyle.css" />
Internal Style Sheet :
An internal style sheet should be used when a single document has a unique style. Internal styles sheet needs to put in the head section of an HTML page, by using the <style> tag, like this:
Inline Styles :
If only a small piece of code has to be styled then inline style sheets can be used.
An inline style loses many of the advantages of style sheets by mixing content with presentation.
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>