add css external to html code example

Example 1: add css file to html

/*
Adding css file into html document
*/

<link rel="stylesheet" type="text/css" href="yourstylesheetname.css">  /* add this line into head tag of the file with change in file name. */

/*
I hope it will help you.
Namaste
*/

Example 2: css without separate file

just add any style inside the first <p> or other element tag using style=" ;" 
<p style="font-size: xx-large;">test</p>