Check out example codes for "how to add a css file in html". It will help you in understanding the concepts better.

Code Example 1

<!DOCTYPE html>
<html>
<head>

  <link rel="stylesheet" href="styles.css">

</head>
<body>

<h1>This is a heading</h1>
<p>This is a paragraph.</p>

</body>
</html>

Code Example 2

<!DOCTYPE html>
<html>
<head>

  <link rel="stylesheet" href="styles.css">

</head>
<body>

<h1>This is a heading</h1>
<p>This is a paragraph.</p>

</body>
</html>

Code Example 3

<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" type="text/css" 
  href="mystyle.css">
</head>
<body>

<h1>This is a heading</h1>

  <p>This is a paragraph.</p>

</body>
</html>

Code Example 4

<head>
	<link rel='stylesheet' href='style.css'>
</head>

Code Example 5

<html>
  <head>
    <link rel="stylesheet" type="text/css" href="mystyle.css"></link>
  </head>

  <body>

Code Example 6

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

Learn ReactJs, React Native from akashmittal.com