The filename can be gotten from the cPath (category path) shown in the address bar when on the listing page. It includes the id of the top category and each subcat in the path.
c_14_21_22.css
The CSS code
.dc.prod_c1 {display: none;}
means that elements with class tags of class="dc prod_c1" will not be displayed.
Ordinarily you would want to add some higher-level tags (like #productListing) to be sure the effects are limited to this case, but since this stylesheet is only applied to this page, that is not necessary.
Standard Zen Cart class/id tags are generally named meaningfully so you can get at least a basic understanding of their purpose, but Template Monster hacks out many of those names and adds many, many cryptic tags which require close inspection of the code to understand. In some cases they remove all identifiers so an element cannot be addressed individually in their template. That's one reason for TM's reputation in this forum.