There are three method to insert to apply css style sheet into html page.
(1) External CSS
(2) Internal CSS
(3) in-line CSS
External CSS Method :
External style sheets are styles that can be applied to as many web pages as you like that are on the same website. The external css file which you want to include in html page shold be write between <head> </head> tags.
<link rel="stylesheet" type="text/css" href="style.css" />
In above example style.css is external valid css file. External css file should not include html tag like <tile>.<head>,<body> etc.
Internal CSS Method :
Generally an internal style sheet is used or placed within the web page where you want to apply style sheet.
The styles are placed within the openning and closing <head> tags.
in-line CSS Method :
You have need to use “style” attribute within the relevant HTML tag where you want in-line css method.
Now, it is cleared from above that how to insert css stylesheet into web page or how css style is called from page.