The menu is an <ul> (unordered list):

<div id="mainmenus">
	<ul id="mainmenu_1">
		<li id="mainmenu_1-1" class="e-1 odd first current_page">
			<a href="/" title="Home">
			<span>Home</span>
			</a>
		</li>
		<li id="mainmenu_1-2" class="e-2 even middle">
			<a href="/properties" title="Properties">
			<span>Properties</span>
			</a>
		</li>
		<li id="mainmenu_1-3" class="e-3 odd middle">
			<a href="/about" title="About Us">
			<span>About Us</span>
			</a>
		</li>
	</ul>
</div>

The <li> of the current page has a current_page class:

Menu with the current page Home highlighted.