CSS should be declared External stylesheet code example
Example 1: add stylesheet html
<link rel="stylesheet" type="text/css" href="style.css">
Example 2: stylesheet css
<style></style> or
<link rel="stylesheet" href="style.css">
<link rel="stylesheet" type="text/css" href="style.css">
<style></style> or
<link rel="stylesheet" href="style.css">