How can I make this button?

If you look to the center right of this (http://www.codecademy.com) page, there is an Add Me button.

How can I make this button style with CSS?

Thanks

Have you ever considered using Firebug (or similar debugging tools in other browsers) and its element inspector? Because then you’d have found out that the button consists of this HTML:
<input type="submit" value="Add Me" name="commit" id="invite_request_submit" class="green">
And it even shows you the styles that are applied to this element. So all you’d have to do is copy that.