1. External style
An external style sheet is an ideal choice when a style needs to be applied to many pages. In the case of using an external style sheet, you can change the appearance of the entire site by changing a file. Each page is linked to the style sheet using the <link> tag. <link> tags in (document) head:
<link rel= "stylesheet" type= "Text/css" href= "Path/mycss.css"/>
2. Internal style
When a single document requires a special style, you should use an internal style sheet. You can use the <style> tab to define an internal style sheet in the header of the document.
<style type= "Text/css" >
Style
</style>
3, inline style
Because you want to mix performance and content together, inline styles can lose many of the advantages of the style sheet. Use this method with caution, such as when a style only needs to be applied on one element at a time. To use inline styles, you need to use style attributes in the relevant tags. The Style property can contain any CSS properties.
Inline styles have the highest precedence, followed by internal styles, and external styles have the lowest precedence.