Hi!
I was lacking an active class for the selected post in the widgets list so I made this little script to add it retrospectively.
Append this jQuery-script to the end of your single.php:
<!-- Add active class to Query Posts list -->
<script type="text/javascript">
jQuery.noConflict();
jQuery(document).ready(function() {
jQuery('.posts .post-<?php the_ID(); ?>').addClass('active');
});
</script>
Then add this to your CSS (example):
.widget-container.posts div.active a {
font-weight: bold;
}
Check this out if you don't know how to include jQuery the right way in WP.