There is no reason to create a new override template just to change SIMPLE css for specific categories, or product pages.
What you can do is wrap your category with a div class tag thats unique per the category id. Like this.
Place this code above where the html starts in your category default.php , or override file.
<div class="h<?php echo JRequest::getInt('virtuemart_category_id'); ?>">
THEN, make sure to close it at the bottom. </div>
You can also do the same with the product page.
<div class="h<?php echo JRequest::getInt('virtuemart_product_id'); ?>">
then you can just add specific styles like this.
.h11 .spacer{height:237px;}
^ where the 11 is the category id.