How to highlight a parent page item?

I tried to answer this question just yesterday, could you please try to search before opening a new topic here?

http://wordpress.org/support/topic/97997?replies=2

Sorry, but I followed the instructions here and on the thread mentioned above and it’s not working. I managed to set up my submenu, you can check it out at http://www.ainhoavega.com/prueba . Any suggestions on how to highlight the parent page when you’re on the children page? For example how to highlight “PRUEBA” when you’re in http://www.ainhoavega.com/prueba/subpagina-1 . Which selector should I used or what condition (php). Right now my code for the submenu is:

<h7><?php if(intval($post->post_parent)>0)
{
	while(intval($post->post_parent)>0)
		$post = get_post($post->post_parent);
}
echo '<a href="'.get_permalink($post->ID).'">'.get_the_title($post->ID).'</a>'; ?>:</h7>

<?php
global $wp_query;
if( empty($wp_query->post->post_parent) ) {
$parent = $wp_query->post->ID;
} else {
$parent = $wp_query->post->post_parent;
}
wp_list_pages("title_li=&child_of=$parent");
?>

And the CSS:

#submenu {
  padding-top:12px;
}

#submenu ul {
  margin:0;
  padding:0;
}

#submenu li {
  float:left;
  margin:0;
  padding:0;
  list-style-type:none;
}

#submenu li a {
  display:block;
  padding:0 10px 0 10px;
  font-size:0.9em;
  letter-spacing:1px;
}

* html #submenu a {width:1%;} /* see http://www.positioniseverything.net/explorer/escape-floats.html */

h7 a, h7 a:hover, h7 {color: #fec42d;
	font-weight: bold;
	text-transform: uppercase;
	font-size: 0.9em;
	float: left;
}

#submenu li {
	border-right: 1px dotted #fec42d;
	margin: 0 5px 0 5px;
}

#submenu a {color:#fec42d;}

#submenu li.current_page_item a:link,
#submenu li.current_page_item a:visited,
#submenu li.current_page_item a:hover,
#submenu li.current_page_item a:active,
#submenu a:hover {color:#fec42d;
	font-weight: bold;
	border-right-color: 1px solid #fec42d;
}