Linking CSS to HTML document
The basic purpose of CSS is to allow a web designer to define style declarations and then he can apply those styles to HTML pages applying through selectors.

Linking Style Sheets to HTML
Styles can be linking to an HTML document using one of three methods:
1. Inline Style
2. Embedded Style
3. External Style
How do you connect a CSS styling sheet to an HTML page ?
1. Inline Style
Inline Style is the simplest method of adding CSS styles to your HTML pages. An inline style is applied to an HTML document via its style attribute to specific tags within the document,
For example, If you want to add styles to < p > then you can code like this:
The above declaration will ensure that the paragraph text will be blue. This method can be applied to any HTML element within the < body > .... < /body > of the HTML page.
output

Notice that the text contained within the first < p > paragraph will be Blue color. You can see only that paragraph is affected, and the second paragraph defaults to black.
The major disadvantage of Inline Style is that it is impossible to reuse. Consider restructuring a website that containing hundreds of pages where inline styles litter the markup. You should have to go into every page and change each CSS property individually is a very difficult task.
2. Embedded Style
Embedded Styles allow you to implement any number of CSS styles by placing them between the opening and closing style tags.
You can place Style Tag within the < head > ... < /head > section, just after the < title > tag of your HTML page.
You should start with the opening style tag like the following: