Check out example codes for "css without separate file". It will help you in understanding the concepts better.

Code Example 1

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

Code Example 2

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

Code Example 3

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

<h1>This is a heading</h1>

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

</body>
</html>

Code Example 4

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

Code Example 5

just add any style inside the first <p> or other element tag using style=" ;" 
<p style="font-size: xx-large;">test</p>

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