Like I understand you have to manually enter:
<li <?php if(in_category(5) || is_category(5)){echo 'class="current-cat"';}?>>
for every category that you have, is that right?
But is there a way to do this automatically?
I mean, is there a way to edit ‘category-template.php’ file and do something with wp_list_categories function, that it would automatically generate list with the effect mentioned above?