w3schools.com style sheey code example

Example 1: add stylesheet html

<link rel="stylesheet" type="text/css" href="style.css">

Example 2: how to use css

<link rel="stylesheet" href="stylesheet.css">
<div class="mydiv"></div>
<style>
.mydiv {
background-color: /*Color*/;
color: /*Another color*/;
}
</style>