Use this code:

<TITLE> HTML for DUMMIES - Example</TITLE></HEAD>
<STYLE TYPE="text/css">
H1.punk { color: #00FF00 }
</STYLE>
</HEAD>
<BODY>

<H1>Not green</H1>
<H1 CLASS=punk>Way too green</H1>

</BODY>

And get this result:

Not green

Way too green