Highlight current category without using wp_list_categories

The sidebar on the website I’m working on displays a list of categories.

I need to somehow be able identify the current one and highlight it.

As I also need to display the posts filed under the current category, I think I can’t use wp_list_categories, which would make identifying the current category easy. So I’m using get_the_categories, but so far haven’t found a way to identify the current category.

It would be great to get some help. Here’s the code. I’m applying it on category.php template:

<ul>
<?php
//Here is where I display the categories that need to be displayed. Alright so far.
	$args = array('orderby' => 'id', 'order' => 'ASC', 'child_of' => '4', 'hide_empty' => 0);
	$categories=  get_categories($args);
	foreach ($categories as $category) {
		echo '<li><a  href="' . get_category_link( $category->term_id ) . '"';

// This is my last try to identify the current category and apply the class "sel" to it. That's where I think I'm failing.
		$category = get_category( get_query_var( 'cat' ) );
		$cat_id = $category->cat_ID;
		if($cat_id->cat_ID == $cat->cat_ID){
			echo ' class="sel"';
		}

// The category name
		echo '>' . $category->name . '</a>';
?>

// The posts under the category. This should be displayed only for current category, but it appears to all of them.
                  <ul>
                         <?php
				the_post();
				foreach( ( get_the_category() ) as $category )
				$my_query = new WP_Query('category_name=' . $category->category_nicename . '&orderby=title&order=asc&showposts=100');
				if( $my_query ) {
					while ( $my_query->have_posts() ) {
						$my_query->the_post(); ?>
						<li<?php print ( is_single() && $IDOutsideLoop == $post->ID ) ? ' class="test"' : ''; ?>>
							<a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a>
						</li>
				<?php
					}
				}
				?>
                           </ul>
			</li>
		<?php }
		?>
         </ul>