Check out example codes for "insert 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

<style>
#panel{
      height: 60%;
      margin-top: 7%;
      margin-left: 10%;
      margin-right: 10%;
      font-family: myriad-pro, sans-serif;
      font-style: normal;
      font-weight: 300;
    }
</style>

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