Specify Li Class Category

Hi there,

Please help me, and teach me how to do this:
– How to specifi my categories in li class?
– Where should i enter in site? What file to edit?

The theme author said to me:
“You have to specify it in list class i.e.<li class=”web-design ” /> If item have more than one category you have to write all category in list class. i.e. <li class=”graphic-design web-design ” /> So these item appear in graphics design and web design category filter.”