NEWBIE PHP Nav bar question

I made a layout. The nav bar is very simple.

<div id="nav">

	<a href="index.php">Home</a>
	<a href="about.php">About</a>
	<a href="portfolio.php">Portfolio</a>
	<a href="contact.php">Contact</a>
	<a href="login.php">Login</a> - <a href="register.php">Sign Up</a>

</div> &lt!-- end #nav -->

My question is, where are the parameters that distinguish the size of these "buttons".

If you goto my site,

http://www.logick.xp3.biz

You will see what I am talking about. Anyone have any idea?
It deff isnt in the styles.css or in the nav.php
I dont remember making these parameters, so is this some kind of default?