How did CNN do this on their site?

[liunx]

There is an effect that happens on the cnn.com site that, for
some reason, I cannot figure out how to duplicate. Now doubt it's very basic, but please bear with me.

If you go to their site, you will notice that every text link rolls over between underlined and not underlined. Is this a CSS thing or basic HTML thing that I'm missing? How is it done?

Thanks in advance.It is CSS, and here it is...

<style type="text/css">
A:link, A:active, A:visited {
color:darkblue;
text-decoration:underline;
}
A:hover {
color:darkred;
text-decoration:none;
}
</style>