Highlighting current page

Hi. Before I start, I am not using the listpages functionality which I know allows easy page highlighting.

In a sidebar, I am displaying the child pages of a parent page. The parent page title is also a link. However, when you are on that page, it is not highlighted like the others. I’ll show the code I’m using and maybe someone can help me. Thanks

<?php
  if($post->post_parent) {
  $children = wp_list_pages("title_li=&child_of=".$post->post_parent."&echo=0");
  $titlenamer = get_the_title($post->post_parent);
  }

  else {
  $children = wp_list_pages("title_li=&child_of=".$post->ID."&echo=0");
  $titlenamer = get_the_title($post->ID);
  }
  if ($children) { ?>
	<div class="subNav">
		<h2>More pages&hellip;</h2>
		<?php $parent_title = get_the_title($post->post_parent);?>
		<h3><a href="<?php echo get_permalink($post->post_parent) ?>">Introduction</a></h3>
		<ul>
			<?php echo $children; ?>
		</ul>
	</div>
<?php } ?>

so it’s the <h3>Introduction</h3> that needs to highlight if I’m on that page. I need to add a class or an ID, whatever.