CSS Internal Styles
CSS enclosed in <style></style> tags within an HTML document functions like an external stylesheet, except that
it lives in the HTML document it styles instead of in a separate file, and therefore can only be applied to the
document in which it lives. Note that this element must be inside the <head> element for HTML validation (though it
will work in all current browsers if placed in body).
<html>
<head>
<style>
h1 {
color: green;
text-decoration: underline;
}
p {
font-size: 25px;
font-family: 'Trebuchet MS', sans-serif;
}
</style>
</head>
<body>
<h1>Hello world!</h1>
<p>I like CSS</p>
</body>
</html>