Check out example codes for "add css". It will help you in understanding the concepts better.

Code Example 1

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

Code Example 2

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

Code Example 3

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

Code Example 4

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

Code Example 5

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

Code Example 6

<!-- External CSS -->
<!-- External styles are defined within the <link> element, inside the <head> section of an HTML page: -->
<!--  
body {
  background-color: lightblue;
}

h1 {
  margin-left: 20px;
}
-->
<head>
<link rel="stylesheet" type="text/css" href="mystyle.css">
</head>
<body>
  <h1>Heading Text</h1>
</body>

<!-- Internal CSS -->
<!-- Internal styles are defined within the <style> element, inside the <head> section of an HTML page: -->
<head>
<style>
body {
  background-color: linen;
}

h1 {
  color: maroon;
  margin-left: 40px;
}
</style>
</head>
<body>
  <h1>Heading text</h1>
</body>

<!-- Inline CSS -->
<!-- Inline styles are defined within the "style" attribute of the relevant element: -->
<body>
  <h1 style="color:blue;text-align:center;">Heading Text</h1>
  <p style="color:red;">Paragraph Text.</p>
</body>

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